Derivatives of Quotients
Example:
y = sqrt(x) / (x3 - x - 2)
The first thing to notice when finding the derivative of this function
is that it is a quotient, as shown below:
| y |
= |
sqrt(x) |
 |
| x3 - x - 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,
| y |
= |
sqrt(x) |
|
| x3 - x - 2 |
we can think of as
| y |
= |
f(x) |
|
| g(x) |
So the derivative is
| y' |
= ( |
f(x) |
)' |
|
| g(x) |
| |
= |
f '(x) |
g(x) |
- |
f(x) |
g '(x) |
|
| ( g(x) )2 |
| |
= |
( sqrt(x) )' |
( x3 - x - 2 ) |
- |
( sqrt(x) ) |
( x3 - x - 2 )' |
|
| ( x3 - x - 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
so the finished derivative is
| y' |
= |
( (1/2)*x-1/2 ) |
( x3 - x - 2 ) |
- |
( sqrt(x) ) |
( 3*x2 - 1 - 0 ) |
|
| ( x3 - x - 2 )2 |
| |
= |
(1/2)*x-1/2 (x3 - x - 2) - sqrt(x) (3*x2 - 1) |
|
| (x3 - x - 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: Sat Apr 19 13:32:31 2025
Comments to Gavin LaRose
glarose@umich.edu
©2001 Gavin LaRose,
University of Michigan Math Dept.