Sometimes, we want to multiply a number by itself several times. For example, if we are trying to guess someone’s password, we may want to know how many 5-letter sequences are possible. Following our lessons on combinatorics (see here), we know that there are possibilities. But we may want an easier way to write this down. The solution is to use exponents. In general,
Rule for Positive Exponents
Using this rule, we can rewrite our earlier expression as simply We call 26 the base and we call 5 the exponent or power. And in general, for , is the base and is the exponent. In English, we say this is “b to the n-th power.” So we would say that is 26 to the 5th power.
Now, we can take any number and raise it to the power of any positive integer simply by multiplying the number by itself that many times. So, we have:
We can even do this for irrational numbers, like :
But we can also have negative exponents. When we take a negative exponent, we use the following formula:
Rule for Negative Exponents
In essence, we flip the base and then take a normal exponent. Here are some examples:
Finally, if we raise anything (other than 0) to the 0th power, we get 1. In other words,
Rule for the 0th Power
Now, there are some rules for how different things with exponents can be combined.
Multiplication and Division Rules for Exponents
Exponent Rule for Exponents
Simplify the following expressions:
by the Multiplication Rule for Exponents.
or by the Division Rule for Exponents.
We can actually solve this problem two ways. First, we could solve it just by calculating: Second, we could solve it by our formulas: so by our Exponent Rule for Exponents. Thus, by our Division Rule for Exponents.
by the Exponent Rule for Exponents.
by the Rule for the 0th Power.
by the Exponent Rule for Exponents and either just directly calculating or by using the Division Rule for Exponents: