Derivatives of Quotients
Example:
Q = (p - 1/2)8 / (p + ln(3))2
The first thing to notice when finding the derivative of this function
is that it is a quotient, as shown below:
| Q |
= |
(p - 1/2)8 |
 |
| (p + ln(3))2 |
The Derivative Rule for Quotients:
The derivative of a quotient is the derivative of the numerator
times the denominator minus the numerator times the derivative of the
denominator, all divided by the denominator squared.
If
| |
z |
= ( |
f(x) |
) |
|
| g(x) |
then the derivative of
z is
| |
z ' |
= ( |
f(x) |
)' |
|
| g(x) |
| |
|
= |
f '(x) g(x) |
- |
f(x) g '(x) |
|
|
|
( g(x) )2 |
So our example,
| Q |
= |
(p - 1/2)8 |
|
| (p + ln(3))2 |
we can think of as
| Q |
= |
f(p) |
|
| g(p) |
So the derivative is
| Q' |
= ( |
f(p) |
)' |
|
| g(p) |
| |
= |
f '(p) |
g(p) |
- |
f(p) |
g '(p) |
|
| ( g(p) )2 |
| |
= |
( (p - 1/2)8 )' |
( (p + ln(3))2 ) |
- |
( (p - 1/2)8 ) |
( (p + ln(3))2 )' |
|
| ( (p + ln(3))2 )2 |
and we just need to know each of the derivatives on the right-hand
side of the equation. In this case these are
| ( (p - 1/2)8 )' |
= |
8*(p - 1/2)7 (1 - 0) |
(by the chain rule) |
| ( (p + ln(3))2 )' |
= |
2*(p + ln(3)) (1 + 0) |
(by the chain rule) |
so the finished derivative is
| Q' |
= |
( 8*(p - 1/2)7 (1 - 0) ) |
( (p + ln(3))2 ) |
- |
( (p - 1/2)8 ) |
( 2*(p + ln(3)) (1 + 0) ) |
|
| ( (p + ln(3))2 )2 |
| |
= |
8*(p - 1/2)7 (p + ln(3))2 - 2*(p - 1/2)8 (p + ln(3)) |
|
| ((p + ln(3))2)2 |
![[]](/images/boxby.gif)
additional explanation for the quotient rule
see another quotient rule example
practice gateway test
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Page Generated: Wed Feb 11 10:38:11 2026
Comments to Gavin LaRose
glarose@umich.edu
©2001 Gavin LaRose,
University of Michigan Math Dept.