
## Section2.8Simplifying Expressions

###### ObjectivesPCC Course Content and Outcome Guide

We know that if we have two apples and add three more, then our result is the same as if we'd had three apples and added two more. In this section, we'll formally define and extend these basic properties we know about numbers to variable expressions.

### Subsection2.8.1Identities and Inverses

We will start with some definitions. The number $0$ is called the additive identity. If the sum of two numbers is the additive identity, $0\text{,}$ these two numbers are called additive inverses. For example, $2$ is the additive inverse of $-2\text{,}$ and the additive inverse of $-2$ is $2\text{.}$

Similarly, the number $1$ is called the multiplicative identity. If the product of two numbers is the multiplicative identity, $1\text{,}$ these two numbers are called multiplicative inverses. For example, $2$ is the multiplicative inverse of $\frac{1}{2}\text{,}$ and the multiplicative inverse of $-\frac{2}{3}$ is $-\frac{3}{2}\text{.}$ The multiplicative inverse is also called reciprocal.

### Subsection2.8.2Introduction to Algebraic Properties

##### Commutative Property

When we compute the area of a rectangle, we generally multiply the length by the width. Does the result change if we multiply the width by the length?

We can see $3\cdot2=2\cdot3\text{.}$ If we denote the length of a rectangle with $L$ and the width with $W\text{,}$ this implies $LW=WL\text{.}$ This is referred to as the commutative property of multiplication. The commutative property also applies to addition, as in $1+2=2+1\text{,}$ where it is called the commutative property of addition. However, there is no commutative property of subtraction or division, as $2-1\ne1-2\text{,}$ and $\frac{4}{2}\ne\frac{2}{4}\text{.}$

##### Associative Property

Let's extend that example to a rectangular prism with length $L=4\text{ cm}\text{,}$ width $W=3\text{ cm}\text{,}$ and height $H=2\text{ cm}\text{.}$ To compute the volume of this solid, we multiply the length, width and height, which we write as $LWH\text{.}$

In the following figure, on the left side, we multiply the length and width first, and then multiply the height; on the right side, we multiply the width and height first, and then multiply the length. Let's compare the products.

We can see $(LW)H=L(WH)\text{.}$ This is known as the associative property of multiplication. The associative property also applies to addition, as in $(1+2)+3=1+(2+3)\text{,}$ which is called the associative property of addition. However, there is no associative property of subtraction, as $(3-2)-1\ne3-(2-1)\text{.}$

##### Distributive Property

The final property we'll explore is called the distributive property, which involves both multiplication and addition. To conceptualize this property, let's consider what happens if we buy 3 boxes that each contain one apple and one pear. This will have the same total cost as if we'd bought 3 apples and 3 pears. We write this algebraically:

\begin{equation*} 3(a+p)=3a+3p\text{.} \end{equation*}

Visually, we can see that it's just a means of re-grouping: $3(\apple+ \pear) = 3(\apple)+ 3(\pear)\text{.}$

### Subsection2.8.3Summary of Algebraic Properties

Let's practice these properties in the following exercises.

### Subsection2.8.4Applying the Commutative, Associative, and Distributive Properties

##### Like Terms

One of the main ways that we will use the commutative, associative, and distributive properties is to simplify expressions. In order to do this, we need to recognize like terms. Two terms are considered like terms if they contain the same variable raised to the same exponent. Here's a table comparing like terms and non-like terms:

 Like Terms Non-Like Terms $7x,2x$ $7x,7y$ $-5xy,\frac{1}{3}xy$ $-5x^2,-4x$ $4y^3,y^3$ $3x,4$ $3,-10$ $2xy,5y$
##### Combining Like Terms

We combine like terms when we take $2a+3a$ and write the result as $5a\text{.}$ The formal process actually involves invoking the distributive property, as we obtain:

\begin{align*} 2a+3a \amp=(2+3)a\\ \amp=5a \end{align*}

In practice, it's helpful to think of this as having $2$ of an object and then an additional $3$ of that same object. In total, we then have $5$ of that object.

###### Example2.8.7

Where possible, simplify the following expressions by combining like terms.

1. $6c+12c-5c$

2. $-5q^2-3q^2$

3. $-3x-5y+4x$

4. $2x-3y+4z$

Solution

1. All three terms are like terms, so they may combined. We combine them two at a time:

\begin{align*} 6c+12c-5c \amp=18c-5c\\ \amp=13c \end{align*}
2. The two terms $-5q^2$ and $-3q^2$ are like terms, so we may combine them:

\begin{align*} -5q^2-3q^2 \amp=-8q^2 \end{align*}
3. The two terms $-3x$ and $4x$ are like terms, while the other term is different. Using the associative and commutative properties of addition in the first step allows us to place the two like terms next to each other, and then combine them:

\begin{align*} -3x-5y+4x \amp=-3x+4x+(-5y)\\ \amp=x-5y \end{align*}
4. The expression $2x-3y+4z$ cannot be simplified as there are no like terms.

###### Remark2.8.8

The expression $x$ represents $1x$ and the expression $-x$ represents $-1x\text{,}$ but we don't write either the “$1$” or the “$-1$” as each is implied. However, it's helpful when combining like terms to remember that $x=1x$ and $-x=-1x\text{.}$

When we add an expression like $4x-5$ to an expression like $3x-7\text{,}$ we write them as follows:

\begin{equation*} (4x-5)+(3x-7) \end{equation*}

In order to remove the given sets of parentheses and apply the commutative property of addition, we will rewrite the subtraction operation as “adding the opposite”:

\begin{equation*} 4x+(-5)+3x+(-7) \end{equation*}

At this point we can apply the commutative property of addition and then combine like terms. Here's how the entire problem will look:

\begin{align*} (4x-5)+(3x-7)\amp=4x+(-5)+3x+(-7)\\ \amp=4x+3x+(-5)+(-7)\\ \amp=7x+(-12)\\ \amp=7x-12 \end{align*}
###### Remark2.8.9

Once we get more comfortable simplifying such expressions, we will simply write the following:

\begin{equation*} (4x-5)+(3x-7)=7x-12 \end{equation*}
###### Example2.8.10

Use the associative, commutative, and distributive properties to simplify the following expressions as much as possible.

1. $(2x+3)+(4x+5)$

2. $(-5x+3)+(4x-7)$

Solution

1. We will remove parentheses, and then combine like terms:

\begin{align*} (2x+3)+(4x+5) \amp=2x+3+4x+5\\ \amp=2x+4x+3+5\\ \amp=6x+8 \end{align*}
2. We will remove parentheses, and then combine like terms::

\begin{align*} (-5x+3)+(4x-7)\amp=-5x+3+4x+(-7)\\ \amp=7x+(-4)\\ \amp=7x-4 \end{align*}
##### Applying the Distributive Property with Negative Coefficients

Applying the distributive property in an expression such as $2(3x+4)$ is fairly straightforward, in that this becomes $2(3x)+2(4)$ which we then simplify to $6x+8\text{.}$ Applying the distributive property is a little trickier when subtraction or a negative constant is involved, for example, with the expression $2(3x-4)\text{.}$ Recalling that subtraction is defined as “adding the opposite,” we can change the subtraction of positive $4$ to the addition of negative $4\text{:}$

\begin{equation*} 2\big(3x+(-4)\big) \end{equation*}

Now when we distribute, we obtain:

\begin{equation*} 2(3x)+2(-4) \end{equation*}

As a final step, we see that this simplifies to:

\begin{equation*} 6x-8 \end{equation*}
###### Remark2.8.11

We can also extend the distributive property to one involving subtraction, which states that $a(b-c)=ab-ac\text{.}$ With this property, we would simplify $2(3x-4)$ more efficiently:

\begin{align*} 2(3x-4) \amp=2(3x)-2(4)\\ \amp=6x-8 \end{align*}

In general, we will use this approach.

###### Example2.8.12

Apply the distributive property to each expression and simplify it as much as possible.

1. $-3(5x+7)$

2. $2(-4x-1)$

Solution

1. We will distribute $-3$ to the $5x$ and $7\text{:}$

\begin{align*} -3(5x+7)\amp=-3(5x)+(-3)(7)\\ \amp=-15x-21 \end{align*}
2. We will distribute $2$ to the $-4x$ and $-1\text{:}$

\begin{align*} 2(-4x-1)\amp=2(-4x)-2(1)\\ \amp=-8x-2 \end{align*}
##### Subtracting Expressions

To subtract one expression from another expression, such as $(5x+9)-(3x+2)\text{,}$ we will again rely on the fact that subtraction is defined as “adding the opposite.” To add the opposite of an expression, we will technically distribute a constant factor of $-1$ and simplify from there:

\begin{align*} (5x+9)-(3x+2)\amp=(5x+9)+(-1)(3x+2)\\ \amp=5x+9+(-1)(3x)+(-1)(2)\\ \amp=5x+9+(-3x)+(-2)\\ \amp=2x+7 \end{align*}
###### Remark2.8.14

The above example demonstrates how we apply the distributive property in order to subtract two expressions. But in practice, it can be pretty cumbersome. A shorter (and often clearer) approach is to instead subtract every term in the expression we are subtracting, which is shown like this:

\begin{align*} (5x+9)-(3x+2)\amp=5x+9-3x-2\\ \amp=2x+7 \end{align*}

In general, we'll use this approach.

###### Example2.8.15

Use the associative, commutative, and distributive properties to simplify the following expressions as much as possible.

1. $(-6x+4)-(3x-7)$

2. $(-2x-5)-(-4x-6)$

Solution

1. We will remove parentheses using the distributive property, and then combine like terms:

\begin{align*} (-6x+4)-(3x-7) \amp=-6x+4-3x-(-7)\\ \amp=-6x+4-3x+7\\ \amp=-9x+11 \end{align*}
2. We will remove parentheses using the distributive property, and then combine like terms:

\begin{align*} (-2x-5)-(-4x-6)\amp=-2x-5-(-4x)-(-6)\\ \amp=-2x-5+4x+6\\ \amp=2x+1 \end{align*}

### Subsection2.8.5The Role of the Order of Operations in Applying the Commutative, Associative, and Distributive Properties

When simplifying an expression such as $3+4(5x+7)\text{,}$ we need to respect the order of operations. Since the terms inside the parentheses are not like terms, there is nothing to simplify there. The next highest priority operation is multiplying the $4$ by $(5x+7)\text{.}$ This must be done before anything happens with the adding of that $3\text{.}$ We cannot say $3+4(5x+7)=\highlight{7}(5x+7)\text{,}$ because that would mean we treated the addition as having higher priority than the multiplication.

So to simplify $3+4(5x+7)\text{,}$ we will first examine the multiplication of $4$ with $(5x+7)\text{,}$ and here we may apply the distributive property. After that, we will use the commutative and associative properties:

\begin{align*} 3+4(5x+7)\amp=3+4(5x)+4(7)\\ \amp=3+20x+28\\ \amp=20x+3+28\\ \amp=20x+31 \end{align*}
###### Example2.8.16

Simplify the following expressions using the commutative, associative, and distributive properties.

1. $4-(3x-9)$

2. $5x+9(-2x+3)$

3. $5(x-9)+4(x+4)$

Solution

1. We will remove parentheses using the distributive property, and then combine like terms:

\begin{align*} 4-(3x-9) \amp=4-3x-(-9)\\ \amp=4-3x+9\\ \amp=-3x+13 \end{align*}
2. We will remove parentheses using the distributive property, and then combine like terms:

\begin{align*} 5x+9(-2x+3)\amp=5x+9(-2x)+9(3)\\ \amp=5x-18x+27\\ \amp=-13x+27 \end{align*}
3. We will remove parentheses using the distributive property, and then combine like terms:

\begin{align*} 5(x-9)+4(x+4)\amp=5x-45+4x+16\\ \amp=9x-29 \end{align*}

### Subsection2.8.6Rules of Exponents and Simplifying

In Section 2.7, we introduced three exponent rules. We continue to use these rules when simplifying expressions. Sometimes though, students incorrectly apply “rules” of exponents where they have misremembered the actual rule. Let's summarize what we can and cannot do.

When we add/subtract two expressions, we can only combine like terms. For example:

• $3x-x=2x$

• $t^2+t^2=2t^2$

• $q^2+q$ cannot be combined.

However, we can multiply two expressions regardless of whether or not they are like terms. For example:

• $x\cdot x=x^2$

• $t^2\cdot t^3=t^5$

• $(q^2)(q)=q^3$

Consider:

• When we combine like terms that have a variable, the exponent doesn't change, as in $x^2+x^2=2x^2\text{.}$

• When we multiply powers of a variable that use the same variable, the exponent will change, as in $(x^2)(x^2)=x^4\text{.}$

• We cannot combine “unlike terms,” as something like $x^2+x$ is as simplified as it can be.

• We can multiply powers with different exponents, as in $(x^2)(x)=x^3\text{.}$

The next few examples test your understanding of these concepts.

###### Example2.8.18

Simplify the following expressions using the rules of exponents and the distributive property.

1. $3x^2+2x+x^2$

2. $(3x^2)(2x)(x^2)$

3. $2x(3x+4)$

4. $x^3-3x^2(5x-2)$

Solution

1. We will combine like terms $3x^2$ and $x^2\text{:}$

\begin{align*} 3x^2+2x+x^2\amp=4x^2+2x \end{align*}
2. We will apply the Product Rule:

\begin{align*} (3x^2)(2x)(x^2)\amp=6x^5 \end{align*}
3. To simplify $2x(3x+4)\text{,}$ we want to first distribute $2x\text{,}$ and then we can apply the Product Rule:

\begin{align*} 2x(3x+4)\amp=2x(3x)+2x(4)\\ \amp=6x^2+8x \end{align*}
4. We will use the distributive property first, apply the Product Rule, and combine like terms:

\begin{align*} x^3-3x^2(5x-2)\amp=x^3-3x^2(5x)-(-3x^2)(2)\\ \amp=x^3-15x^3+6x^2\\ \amp=-14x^3+6x^2 \end{align*}

### Subsection2.8.7Exercises

These exercises involve the concepts of like terms and the commutative, associative, and distributive properties.

###### 1

The additive inverse of $-3$ is

###### 2

The additive inverse of $-1$ is

###### 3

The multiplicative inverse of $2$ is

###### 4

The multiplicative inverse of $4$ is

###### 5

Use the associative property of addition to write an equivalent expression to ${n+\left(12+a\right)}\text{.}$

###### 6

Use the associative property of addition to write an equivalent expression to ${p+\left(54+q\right)}\text{.}$

###### 7

Use the associative property of addition to write an equivalent expression to ${12+\left(19+x\right)}\text{.}$

###### 8

Use the associative property of addition to write an equivalent expression to ${5+\left(8+y\right)}\text{.}$

###### 9

Use the associative property of multiplication to write an equivalent expression to ${10\!\left(9t\right)}\text{.}$

###### 10

Use the associative property of multiplication to write an equivalent expression to ${6\!\left(3a\right)}\text{.}$

###### 11

Use the commutative property of addition to write an equivalent expression to ${c+21}\text{.}$

###### 12

Use the commutative property of addition to write an equivalent expression to ${n+4}\text{.}$

###### 13

Use the commutative property of addition to write an equivalent expression to ${5c+73}\text{.}$

###### 14

Use the commutative property of addition to write an equivalent expression to ${9n+16}\text{.}$

###### 15

Use the commutative property of addition to write an equivalent expression to ${4\!\left(p+82\right)}\text{.}$

###### 16

Use the commutative property of addition to write an equivalent expression to ${8\!\left(x+47\right)}\text{.}$

###### 17

Use the commutative property of multiplication to write an equivalent expression to ${12y}\text{.}$

###### 18

Use the commutative property of multiplication to write an equivalent expression to ${77t}\text{.}$

###### 19

Use the commutative property of multiplication to write an equivalent expression to ${42+10a}\text{.}$

###### 20

Use the commutative property of multiplication to write an equivalent expression to ${8+5c}\text{.}$

###### 21

Use the commutative property of multiplication to write an equivalent expression to ${6\!\left(m+79\right)}\text{.}$

###### 22

Use the commutative property of multiplication to write an equivalent expression to ${4\!\left(b+21\right)}\text{.}$

###### 23

Use the distributive property to write an equivalent expression to ${2\!\left(n+7\right)}$ that has no grouping symbols.

###### 24

Use the distributive property to write an equivalent expression to ${8\!\left(p+2\right)}$ that has no grouping symbols.

###### 25

Use the distributive property to write an equivalent expression to ${-7\!\left(x-1\right)}$ that has no grouping symbols.

###### 26

Use the distributive property to write an equivalent expression to ${-2\!\left(y+8\right)}$ that has no grouping symbols.

###### 27

Use the distributive property to write an equivalent expression to ${-\left(t+3\right)}$ that has no grouping symbols.

###### 28

Use the distributive property to write an equivalent expression to ${-\left(a-4\right)}$ that has no grouping symbols.

###### 29

Use the distributive property to simplify ${10+3\!\left(4+3c\right)}$ completely.

###### 30

Use the distributive property to simplify ${3+2\!\left(10+6x\right)}$ completely.

###### 31

Use the distributive property to simplify ${10-4\!\left(-8+t\right)}$ completely.

###### 32

Use the distributive property to simplify ${10-7\!\left(-1-9n\right)}$ completely.

###### 33

Use the distributive property to simplify ${6-\left(6-7p\right)}$ completely.

###### 34

Use the distributive property to simplify ${3-\left(-6+9x\right)}$ completely.

###### 35

Use the distributive property to simplify ${9-\left(3y+3\right)}$ completely.

###### 36

Use the distributive property to simplify ${6-\left(-3t-10\right)}$ completely.

###### 37

Use the distributive property to simplify ${{\frac{3}{2}}\!\left(-10+a\right)}$ completely.

###### 38

Use the distributive property to simplify ${{\frac{9}{2}}\!\left(-10+3c\right)}$ completely.

###### 39

Use the distributive property to simplify ${{\frac{2}{3}}\!\left(-10+{\frac{3}{4}}c\right)}$ completely.

###### 40

Use the distributive property to simplify ${{\frac{4}{5}}\!\left(-10+{\frac{3}{2}}y\right)}$ completely.

###### 41

The expression ${n+m+y}$ would be ambiguous if we did not have a left-to-right reading convention. Use grouping symbols to emphasize the order that these additions should be carried out.

Use the associative property of addition to write an equivalent (but different) algebraic expression.

###### 42

The expression ${p+b+q}$ would be ambiguous if we did not have a left-to-right reading convention. Use grouping symbols to emphasize the order that these additions should be carried out.

Use the associative property of addition to write an equivalent (but different) algebraic expression.

###### 43

A student has (correctly) simplified an algebraic expression in the following steps. Between each pair of steps, identify the algebraic property that justifies moving from one step to the next.

$\phantom{={}}{2\!\left(x+9\right)+5x}$

?

commutative property of addition

commutative property of multiplication

associative property of addition

associative property of multiplication

distributive property

$={\left(2x+18\right)+5x}$

?

commutative property of addition

commutative property of multiplication

associative property of addition

associative property of multiplication

distributive property

$={\left(18+2x\right)+5x}$

?

commutative property of addition

commutative property of multiplication

associative property of addition

associative property of multiplication

distributive property

$={18+\left(2x+5x\right)}$

?

commutative property of addition

commutative property of multiplication

associative property of addition

associative property of multiplication

distributive property

$={18+\left(2+5\right)x}$

$={18+7x}$

?

commutative property of addition

commutative property of multiplication

associative property of addition

associative property of multiplication

distributive property

$={7x+18}$

###### 44

A student has (correctly) simplified an algebraic expression in the following steps. Between each pair of steps, identify the algebraic property that justifies moving from one step to the next.

$\phantom{={}}{7\!\left(y+4\right)+3y}$

?

commutative property of addition

commutative property of multiplication

associative property of addition

associative property of multiplication

distributive property

$={\left(7y+28\right)+3y}$

?

commutative property of addition

commutative property of multiplication

associative property of addition

associative property of multiplication

distributive property

$={\left(28+7y\right)+3y}$

?

commutative property of addition

commutative property of multiplication

associative property of addition

associative property of multiplication

distributive property

$={28+\left(7y+3y\right)}$

?

commutative property of addition

commutative property of multiplication

associative property of addition

associative property of multiplication

distributive property

$={28+\left(7+3\right)y}$

$={28+10y}$

?

commutative property of addition

commutative property of multiplication

associative property of addition

associative property of multiplication

distributive property

$={10y+28}$

###### 45

The number of students enrolled in math courses at Portland Community College has grown over the years.

The formulas

\begin{aligned}M\amp =0.37x+4.1 \amp \qquad\amp \amp W\amp =0.54x+5.6\end{aligned}

describe the numbers (of thousands) of men and women enrolled in math courses at PCC $x$ years after 2005. Give a simplified formula for the total number $T$ of thousands of students at PCC taking math classes $x$ years after 2005. Be sure to give the entire formula, starting with T=.

###### 46

The number of students enrolled in math courses at Portland Community College has grown over the years.

The formulas

\begin{aligned}M\amp =0.4x+3.1 \amp \qquad\amp \amp W\amp =0.36x+4.8\end{aligned}

describe the numbers (of thousands) of men and women enrolled in math courses at PCC $x$ years after 2005. Give a simplified formula for the total number $T$ of thousands of students at PCC taking math classes $x$ years after 2005. Be sure to give the entire formula, starting with T=.

These exercises involve the rules of exponents.

###### 47

Find the product of the monomial and the binomial.

${-x}\left({x+8}\right)=$

###### 48

Find the product of the monomial and the binomial.

${x}\left({x-4}\right)=$

###### 49

Find the product of the monomial and the binomial.

${8x}\left({6x-9}\right)=$

###### 50

Find the product of the monomial and the binomial.

${9x}\left({-9x+9}\right)=$

###### 51

Find the product of the monomial and the binomial.

${8x^{2}}\left({x-4}\right)=$

###### 52

Find the product of the monomial and the binomial.

${-10x^{2}}\left({x+10}\right)=$

###### 53

Find the product of the monomial and the binomial.

${-7x^{2}}\left({7x^{2}+6x}\right)=$

###### 54

Find the product of the monomial and the binomial.

${4x^{2}}\left({5x^{2}-10x}\right)=$

These exercises involve rules of exponents and combining like terms.

###### 55

Simplify the following expressions if possible.

1) $\displaystyle{ {a^{4}+a^{4}}=}$

2) $\displaystyle{ (a^4)(a^4)=}$

3) $\displaystyle{ {a^{4}+a}=}$

4) $\displaystyle{ (a^4)(a)=}$

###### 56

Simplify the following expressions if possible.

1) $\displaystyle{ {c^{3}+c^{3}}=}$

2) $\displaystyle{ (c^3)(c^3)=}$

3) $\displaystyle{ {c^{3}+c^{2}}=}$

4) $\displaystyle{ (c^3)(c^2)=}$

###### 57

Simplify the following expressions if possible.

1) $\displaystyle{ {3r^{2}+2r^{2}}=}$

2) $\displaystyle{ (3r^{2})(3r^{2})=}$

3) $\displaystyle{ {3r^{2}-r}=}$

4) $\displaystyle{ (3r^{2})(-r)=}$

###### 58

Simplify the following expressions if possible.

1) $\displaystyle{ {-3p^{4}-2p^{4}}=}$

2) $\displaystyle{ (-3p^{4})(-3p^{4})=}$

3) $\displaystyle{ {-3p^{4}+2p^{2}}=}$

4) $\displaystyle{ (-3p^{4})(2p^{2})=}$

###### 59

Simplify the following expressions if possible.

1) $\displaystyle{ {m^{2}+4m^{3}+2m^{2}}=}$

2) $\displaystyle{ (m^{2})(4m^{3})(2m^{2})=}$

###### 60

Simplify the following expressions if possible.

1) $\displaystyle{ {-3p^{3}-4p^{4}+2p^{3}}=}$

2) $\displaystyle{ (-3p^{3})(-4p^{4})(2p^{3})=}$

###### 61

Simplify the following expression.

$\displaystyle{ {3x^{5}\!\left(-3x^{3}\right)^{2}}=}$

###### 62

Simplify the following expression.

$\displaystyle{ {-4y^{3}\!\left(-5y^{5}\right)^{2}}=}$

###### 63

Simplify the following expression.

$\displaystyle{ {-2t^{2}y^{5}\!\left(2t^{5}y^{2}\right)^{5}}=}$

###### 64

Simplify the following expression.

$\displaystyle{ {-2a^{4}m^{2}\!\left(4a^{3}m^{4}\right)^{2}}=}$

###### 65

Simplify the following expression.

$\displaystyle{ (-3c^{5})(2c^{3})-(3c^{4})(4c^{4})=}$

###### 66

Simplify the following expression.

$\displaystyle{ (-3y^{4})(4y^{5})-(y^{5})(-5y^{4})=}$

###### 67

Simplify the following expression.

$\displaystyle{ (5m^{5})\left(4m^{4}\right)^{2}-(m^{5})(5m^{4})=}$

###### 68

Simplify the following expression.

$\displaystyle{ (-2m^{5})\left(3m^{4}\right)^{2}-(5m^{4})(-5m^{5})=}$

###### 69

Simplify the following expression.

$\displaystyle{ (p^{5})\left(2p^{4}\right)^{3} + \left(-3p\right)^{2}(5p^{15})=}$

###### 70

Simplify the following expression.

$\displaystyle{ (2q^{5})\left(-q^{2}\right)^{2}+\left(2q\right)^{4}(-3q^{5})=}$

###### 71

Simplify the following expression.

$\displaystyle{ {\left(-3y^{4}\right)^{3}a^{12}-2\!\left(y^{4}a^{4}\right)^{3}}=}$

###### 72

Simplify the following expression.

$\displaystyle{ {\left(3t^{3}\right)^{3}q^{9}-3\!\left(t^{3}q^{3}\right)^{3}}=}$

These exercises involve the distributive property and rules of exponents.

###### 73

Use the distributive property to write an equivalent expression to ${-5a\!\left(2a-1\right)}$ that has no grouping symbols.

###### 74

Use the distributive property to write an equivalent expression to ${-8c\!\left(9c+8\right)}$ that has no grouping symbols.

###### 75

Use the distributive property to write an equivalent expression to ${-8q^{3}\!\left(q+1\right)}$ that has no grouping symbols.

###### 76

Use the distributive property to write an equivalent expression to ${-8m^{2}\!\left(m+9\right)}$ that has no grouping symbols.

###### 77

Use the distributive property to simplify ${4+3m\!\left(10+6m\right)}$ completely.

###### 78

Use the distributive property to simplify ${10+6p\!\left(8+6p\right)}$ completely.

###### 79

Use the distributive property to simplify ${7q-2q\!\left(-1-2q^{2}\right)}$ completely.

###### 80

Use the distributive property to simplify ${3y-7y\!\left(-7-y^{4}\right)}$ completely.

###### 81

Use the distributive property to simplify ${9t^{3}-3t^{3}\!\left(8-t^{3}\right)}$ completely.

###### 82

Use the distributive property to simplify ${6a^{3}-9a^{3}\!\left(2-a^{4}\right)}$ completely.

###### 83

Fully simplify ${-4\!\left(-2x-7\right)+6\!\left(-9x-1\right)}\text{.}$

###### 84

Fully simplify ${-5\!\left(-8x+1\right)-7\!\left(-4x-3\right)}\text{.}$

###### 85

Fully simplify ${6\!\left(-4x-5\right)+8\!\left(7x-5\right)}\text{.}$

###### 86

Fully simplify ${7\!\left(-2x+9\right)-9\!\left(-2x-8\right)}\text{.}$