Exponents

The exponent of a number says how many times to use the number in a multiplication.

 

8 to the Power 2

In 82 the "2" says to use 8 twice in a multiplication,
so 82 = 8 × 8 = 64

In words: 82 could be called "8 to the power 2" or "8 to the second power", or simply "8 squared"

Exponents are also called Powers or Indices.

Some more examples:

Example: 53 = 5 × 5 × 5 = 125

Example: 24 = 2 × 2 × 2 × 2 = 16

 

Exponents make it easier to write and use many multiplications

Example: 96 is easier to write and read than 9 × 9 × 9 × 9 × 9 × 9

You can multiply any number by itself as many times as you want using exponents.

Try here:

In General

So in general:

an tells you to multiply a by itself,
so there are n of those a's:
  exponent definition

Another Way of Writing It

Sometimes people use the ^ symbol (above the 6 on your keyboard), as it is easy to type.

Example: 2^4 is the same as 24

Negative Exponents

Negative? What could be the opposite of multiplying? Dividing!

So we divide by the number each time, which is the same as multiplying by 1number

Example: 8-1 = 18 = 0.125

We can continue on like this:

Example: 5-3 = 15 × 15 × 15 = 0.008

But it is often easier to do it this way:

5-3 could also be calculated like:

15 × 5 × 5 = 153 = 1125 = 0.008

Negative? Flip the Positive!

negative-exponent

That last example showed an easier way to handle negative exponents:

  • Calculate the positive exponent (an)
  • Then take the Reciprocal (i.e. 1/an)

More Examples:

Negative Exponent   Reciprocal of
Positive Exponent
  Answer
4-2 = 1 / 42 = 1/16 = 0.0625
10-3 = 1 / 103 = 1/1,000 = 0.001
(-2)-3 = 1 / (-2)3 = 1/(-8) = -0.125

What if the Exponent is 1, or 0?

1   If the exponent is 1, then you just have the number itself (example 91 = 9)
     
0   If the exponent is 0, then you get 1 (example 90 = 1)
     
    But what about 00 ? It could be either 1 or 0, and so people say it is "indeterminate".

It All Makes Sense

If you look at that table, you will see that positive, zero or negative exponents are really part of the same (fairly simple) pattern:

Example: Powers of 5
  .. etc..   exponent 5 times larger or smaller
52 5 × 5 25
51 5 5
50 1 1
5-1 15 0.2
5-2 15 × 15 0.04
  .. etc..  

Be Careful About Grouping

To avoid confusion, use parentheses () in cases like this:

With () : (-2)2 = (-2) × (-2) = 4
Without () : -22 = -(22) = - (2 × 2) = -4

With () : (ab)2 = ab × ab
Without () : ab2 = a × (b)2 = a × b × b