Algebra and Trigonometry, 2015a

SECTION 1.2 EXPONENTS AND SCIENTIFIC NOTATION 21
Try It #4
Simplify each expression using the zero exponent rule of exponents.
a. t 7
__
t 7 b.
_(de 2 ) 11
2(de 2 ) c. w 4 · w 2
11
_
Using the Negative Rule of Exponents
w d. _ t 3 · t 4
6 t 2 · t 5
Another useful result occurs if we relax the condition that m > n in the quotient rule even further. For example, can we
simplify
_ h3
? When m < n —that is, where the difference m − n is negative—we can use the negative rule of exponents
5
h
to simplify the expression to its reciprocal.
Divide one exponential expression by another with a larger exponent. Use our example,
_ h3
h . 5
_ h 3
h = __ h · h · h
5 h · h · h · h · h
h · h · h
=
__
h · h · h · h · h
=
1_
h · h
= 1 _
h 2
If we were to simplify the original expression using the quotient rule, we would have
h 3 _
h 5 = h3 − 5
= h −2
Putting the answers together, we have h −2 =
_ 1 . This is true for any nonzero real number, or any variable representing
2
h
a nonzero real number.
A factor with a negative exponent becomes the same factor with a positive exponent if it is moved across the fraction
bar—from numerator to denominator or vice versa.
a −n = 1 _
a
n and an =
We have shown that the exponential expression a n is defined when n is a natural number, 0, or the negative of a natural
number. That means that an is defined for any integer n. Also, the product and quotient rules and all of the rules we
will look at soon hold for any integer n.
the negative rule of exponents
For any nonzero real number a and natural number n, the negative rule of exponents states that
1_
a −n
a −n = 1 _
a
n
Example 5
Using the Negative Exponent Rule
Write each of the following quotients with a single base. Do not simplify further. Write answers with positive exponents.
a.
θ 3 _
θ 10
b. _ z 2 ċ z
z c. _
(−5t 3 ) 4
4 (−5t 3 ) 8
Solution
θ
a.
_
3
θ = θ 3 − 10 = θ −7 =
_ 1
10 θ 7
z
b.
_
2 ∙ z
z = _ z 2 + 1
4 z = _ z 3
4 z = 4 z3 − 4 = z −1 =
_ 1 z
(−5t 3 ) 4
c.
_
(−5t 3 ) = (−5t 3 ) 4 − 8 = (−5t 3 ) −4 =
1_
8 (−5t 3 ) 4