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1.6: Evaluate Numerical and Variable Expressions Involving Powers

Difficulty Level: At Grade Created by: CK-12
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Let’s Think About It

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Casey missed three days of school this week because of a nasty cold. When he returned to school on Thursday he asked his math teacher what he had missed. Miss Brown wrote a problem on a sheet of paper and handed it to Casey. When he arrived home from school Casey looked at his homework which was the following problem:

54+(2)4+12

Casey didn’t know what to do with 54and (2)4. How can he rewrite the problem so that he understands what operations to perform?

In this concept, you will learn how to evaluate numerical expressions involving powers.

Guidance

A numerical expression is an expression made up only of numbers and operations but an expression written with a variable in it, is called a variable expression.

Both a numerical expression and a variable expression can include powers.

A power is the result of multiplying a number by itself one or more times. The number 16 is the fourth power of 2.

2×2×2×2=16. The ‘fourth power of 2’ or ‘2 to the power of 4’ can be written as 24. The number raised to the power is called the base and the number expressing the power is called the exponent. The exponent tells you how many times to multiply the base times itself.63=6×6×6.

Let’s look at an example.

Evaluate the following expression: 

63+52+25

First, expand the powers to see the operations you need to perform. 

63=6×6×6 and 52=5×5
Next, write the expression in expanded form. 

6×6×6+5×5+25

Next, apply the order to operations (PEMDAS) to evaluate the expanded expression.

Then, in order from left to right, multiply: 6×6=36×6=216and write the new expression.

216+5×5+25

Then, multiply: 5×5=25 and write the new expression.

216+25+25

Next, from left to right, add: 216+25=241and write the new expression.

241+25

Then, add:241+25=266 

The answer is 266.

Let’s look at another example.

62+15+3311

First, expand the powers to see the operations you need to perform. 

62=6×6 and 33=3×3×3

Next, write the expression in expanded form.

6×6+15+3×3×311

Next, apply the order to operations (PEDMAS) to evaluate the expanded expression.

Then, in order from left to right multiply: 6×6=36and write the new expression.

36+15+3×3×311

Then, multiply:3×3×3=27and write the new expression. 

36+15+2711

Next, from left to right, add: 36+15=51and write the new expression.  

51+2711

 Then, add:51+2778and write the new expression.

7811

Next, subtract:7811=67

The answer is 67.

Guided Practice

Evaluate the following variable expression whenx=4

2x312

First, substitute the value x=4into the expression.

2(4)312

Next, expand the power.

(4)3=(4×4×4)
Next, write the expression in expanded form.

2(4×4×4)12

Then, perform the operation in the parenthesis.

Multiply:4×4=16×4=64and write the new expression.

2(64)12

Next, multiply: 2(64)=128and write the new expression.

12812

Then, subtract.

12812=116

The answer is 116.

Examples

Example 1

Evaluate the following numerical expression.

2024+1+33

First, expand the powers. 

2×2×2×2 and 3×3×3
 

 Next, write the expression in expanded form. 

202×2×2×2+1+3×3×3

Then, in order from left to right multiply: 2×2×2×2=16and write the new expression.

2016+1+3×3×3

Next, multiply: 3×3×3=27 and write the new expression.

2016+1+27

Then, in order from left to write, subtract: 2016=4 and write the new expression.

4+1+27

Next, add: 4+1=5and write the new expression.

5+27

Then add: \begin{align*}5+27=32\end{align*}5+27=32 

The answer is 32.

Example 2

Evaluate the following variable expression when \begin{align*}m=3\end{align*}m=3and\begin{align*}n=2\end{align*}n=2

\begin{align*}n^5+3m^2-15\end{align*}

n5+3m215

First, substitute \begin{align*}m=3\end{align*}m=3and\begin{align*}n=2\end{align*}n=2into the variable expression.

\begin{align*}2^5+3(3)^2-15\end{align*}

25+3(3)215
Next, expand the powers:\begin{align*}2^5=( 2 \times 2 \times 2 \times 2 \times 2) \ \text{and} \ (3)^2 =(3 \times 3)\end{align*}
25=(2×2×2×2×2) and (3)2=(3×3)
  

Then, write the expression in expanded form.

\begin{align*}2 \times 2 \times 2 \times 2 \times 2 +3 (3 \times 3)-15\end{align*}

2×2×2×2×2+3(3×3)15

Then, perform the operation in the parenthesis.

First, multiply: \begin{align*}(3 \times 3)=(9)\end{align*}(3×3)=(9)and write the new expression.

\begin{align*}2 \times 2 \times 2 \times 2 \times 2 + 3(9)-15\end{align*}

2×2×2×2×2+3(9)15

Next, multiply: \begin{align*}3(9)=27\end{align*}3(9)=27to clear the parenthesis. Write the new expression.

\begin{align*}2 \times 2 \times 2 \times 2 \times 2 +27-15\end{align*}

2×2×2×2×2+2715

Next, multiply:  \begin{align*}2 \times 2 = 4 \times 2 = 8 \times 2 =16 \times 2 =32 \end{align*}2×2=4×2=8×2=16×2=32Write the new expression.

\begin{align*}32+27-15\end{align*}

32+2715

Next, add: \begin{align*}32+27=59\end{align*}32+27=59and write the new expression. 

\begin{align*}59-15\end{align*}

5915
Then, subtract: \begin{align*}59-15=44\end{align*}5915=44 

The answer is 44.

Follow Up

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License: CC BY-NC 3.0

Remember Casey and his confusing homework?

Casey needs to expand the powers so he can see what operations he has to do to evaluate the expression.

First, evaluate the two powers given in the problem.

\begin{align*}5^4= 5 \times 5 \times 5 \times 5 =625 \ \text{and} \ (-2)^4=-2 \times -2 \times-2 \times -2 =16 \end{align*}

54=5×5×5×5=625 and (2)4=2×2×2×2=16

Next, replace the powers in the expression with their values. 

\begin{align*}625+16+12\end{align*}

Then, add.

\begin{align*}625+16=641+12=653\end{align*}

The answer is 653.

Video Review

Explore More

Expand and evaluate each power.

1. \begin{align*}3^3\end{align*}

2. \begin{align*}4^2\end{align*}

3. \begin{align*}(-2)^4\end{align*}

4. \begin{align*}(-8)^2\end{align*}

5. \begin{align*}5^3\end{align*}

6. \begin{align*}2^6\end{align*}

7. \begin{align*}(-9)^2\end{align*}

8. \begin{align*}(-2)^6\end{align*}

Evaluate each numerical expression. Remember to apply PEDMAS to evaluate the expression accurately.

9. \begin{align*}6^2+22\end{align*}

10. \begin{align*}(-3)^3+18\end{align*}

11. \begin{align*}2^3+16-4\end{align*}

12. \begin{align*}(-5)^2-19\end{align*}

13. \begin{align*}(-7)^2+52-2\end{align*}

14. \begin{align*}18+9^2-3\end{align*}

15. \begin{align*}22-3^3+7\end{align*}

Evaluate each variable expression using the given values.

16. \begin{align*}6a+4^2-2\end{align*}, when \begin{align*}a=3\end{align*}

17. \begin{align*}a^3+14\end{align*}, when \begin{align*}a=6\end{align*}

18. \begin{align*}2a^2-16\end{align*}, when \begin{align*}a=4\end{align*}

19. \begin{align*}5b^3+12\end{align*}, when \begin{align*}b=-2\end{align*}

20. \begin{align*}2x^2+52\end{align*}, when \begin{align*}x=4\end{align*}

Vocabulary

Base

Base

When a value is raised to a power, the value is referred to as the base, and the power is called the exponent. In the expression 32^4, 32 is the base, and 4 is the exponent.
Evaluate

Evaluate

To evaluate an expression or equation means to perform the included operations, commonly in order to find a specific value.
Expression

Expression

An expression is a mathematical phrase containing variables, operations and/or numbers. Expressions do not include comparative operators such as equal signs or inequality symbols.
Integer

Integer

The integers consist of all natural numbers, their opposites, and zero. Integers are numbers in the list ..., -3, -2, -1, 0, 1, 2, 3...
Numerical expression

Numerical expression

A numerical expression is a group of numbers and operations used to represent a quantity.
Parentheses

Parentheses

Parentheses "(" and ")" are used in algebraic expressions as grouping symbols.
Power

Power

The "power" refers to the value of the exponent. For example, 3^4 is "three to the fourth power".
substitute

substitute

In algebra, to substitute means to replace a variable or term with a specific value.
Variable Expression

Variable Expression

A variable expression is a mathematical phrase that contains at least one variable or unknown quantity.
Volume

Volume

Volume is the amount of space inside the bounds of a three-dimensional object.

Description

Difficulty Level:

At Grade

Grades:

Date Created:

Dec 19, 2012

Last Modified:

Dec 15, 2015
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