Introduction to Exponents

Written by tutor April G.

The Basics

Exponents are shorthand for repeated multiplication, just like multiplication is a shortened form of repeated addition.

2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 = 2×10 = 20
a + a + a + a + a + a + a + a + a + a = a×10 = 10a

A much easier improvement, right? We do something similar in multiplication using exponents.

In mathematics, we use superscripts to represent the number of times the number is multiplied by itself. These superscripts are the exponents.

2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 = 2¹⁰ = 1,024
a × a × a × a × a × a × a × a × a × a = a¹⁰

Exponents shorten writing out long strings of repeated multiplication.

For example, 3×2×2×3×3×2×2 = 2×2×2×2×3×3×3 = 2⁴3³.

Note: You might also see exponents written out this way: a^10. This is commonly used on computers because it’s easier to type.

Now for the technical math stuff.

In the expression aⁿ, we are saying that a is being multiplied by itself n number of times. We call a the base,
and n is the exponent. The expression an is called a power, and is read as, “a raised to the power of n”
or “a to the nth power.” In my above example of 2¹⁰, 2 is the base, 10 is the exponent (the number of times 2 is
multiplied by itself), and we read it as “2 raised to the 10th power.” Because 2¹⁰ = 1024, 1024 is a power of 2.

Some powers are special because they come up quite frequently. a² can also be read as “a-squared,” and a³ as “a-cubed.”
Also, a¹ = a (which is pretty boring, but still important to know!).

Evaluating Basics

Powers are included in the order of operations.
(PEMDAS) – Parenthesis, Exponents, Division/Multiplication, Addition/Subtraction. Exponents
are pretty high up on the list!

Example: What is the value of 3² + 5⁴? First evaluate 3² = 9 and 5⁴ = 625. Then, add them together,
and the result is 634.
Example: What is the value of -1 × 2⁵? First, evaluate 2⁵ = 32. Then, multiply -1 and 32, and you get a result of -32.

In some cases, you need to plug in values for variables to evaluate.

Example: Evaluate ab² for a = 3 and b = 5. It’s very important to note that this means a × b². Some students get
confused and think that a and b need to be multiplied first, and then square the result. If we were to do that, the problem would be written as
(ab)² instead. According to the order of operations, first the b must be squared, and then the result multiplied by a.
When we substitute the values, we get 3 × 5² = 3 × 25 = 75. The other way, (ab)², would be (3×5)² =
(15)² = 225. Pay extra attention to how the problem is written and follow the order of operations.

Negative Bases

Things get a little tricky when you throw negatives into the mix.

For (-2)², when we write out the multiplication we have (-2) × (-2) = 4. (Remember that when you multiply 2 negatives, you get a
positive product, and when you multiply a positive and a negative you get a negative product.) What happens for (-2)³?
You would get (-2) × (-2) × (-2) = 4 × (-2) = -8. What about (-2)⁴? (-2)⁵? You’ll find that when the base is negative
and the exponent is an even number, the result is positive. If the base is negative and the exponent is an odd number,
the result is negative.

Why did I use parentheses around the -2? Couldn’t you just write -2³? -2⁴?

Take for example (-2)⁴ versus -2⁴. Using our definition of exponents, (-2)⁴ = 16. For -2⁴,
because there are no exponents around the (-2), we are actually saying the same thing as “the opposite of 2⁴“. (Just like -3
is the opposite of 3.) Because 2⁴ = 16, then -2⁴ (“the opposite of 2⁴“) = -16. Those parentheses
become crucial to properly evaluating exponents with negatives! For this reason, I suggest using parentheses when plugging in values to
evaluate to eliminate the confusion.

Negative and Zero Exponents

What about negative exponents? Can zero be an exponent?

First, yes, zero can be an exponent, and it’s a little weird. When the exponent is zero (as in 2⁰), the result is 1. Any base (except zero)
with a zero exponent is equal to 1. 2⁰ = 1, b⁰ = 1, 1929843⁰ = 1. (0⁰ is very bizarre and
we say the result is indeterminate.)

What about negative exponents? If we looked at the negative as meaning “opposite”, and the exponent means repeating a multiplication, then we can ask,
“What is the opposite of multiplication?” Division! Having a negative exponent means how many times we divide one by that number.

Example: 5^-1 = 1 ÷ 5 = 0.2

Example: 5^-3 = 1 ÷ 5 ÷ 5 ÷ 5 = 0.008

An easier way of evaluating 5^-3 would be 5^-3 = 1 ÷ (5×5×5) = 1/5³ = 1/125 = 0.008. In general, a^-n = 1/aⁿ.
So for 4^-2, we can say 4^-2 = 1/4² = 1/16 = 0.0625.

Summary

When evaluating expressions with exponents, there are some important points to remember:

• Follow the order of operations and watch out for common traps.
• Remember that exponents are shorthand for repeated multiplication. 2³ is not the same as 2×3! It means 2×2×2.
• Be careful evaluating exponents with negative bases. Use parenthesis when necessary to help you remember.
• Negative exponents are the same as repeated division of one by a number, or you can use the easy shortcut to evaluate them faster.
• Negative exponents don’t make a number negative! 2^-3 = 1/2³ = 1/8 = 0.125, not -8!

Exponents Practice Quiz