Derivatives of Sums
Example:
R = sqrt((-6)*q5 + 6) - q4
The first thing to notice when finding the derivative of this function
is that it is
the sum of several terms,
as shown in color below:
| R |
= |
( sqrt((-6)*q5 + 6) ) | - |
( q4 ) |
The Derivative Rule for Sums:
The derivative of a sum is the sum of the derivatives.
If
then the derivative of
z is
| |
z' |
= |
( f(x) |
+ |
g(x) )' |
| |
|
= |
f '(x) |
+ |
g'(x) |
So our example,
| R |
= |
( sqrt((-6)*q5 + 6) ) | - |
( q4 ) |
we can think of as
So the derivative is
| R ' |
= ( |
f(q) |
- |
g(q) |
)' |
| |
= |
f '(q) |
- |
g '(q) |
|
| |
= |
( sqrt((-6)*q5 + 6)) ' |
- |
( q4) ' |
|
and we just need to know each of the derivatives on the right-hand
side of the equation. In this case these are
| ( sqrt((-6)*q5 + 6) )' |
= |
(1/2)*((-6)*q5 + 6)-1/2 ((-6)*5*q4 + 0) |
(by the chain rule) |
| ( q4 )' |
= |
4*q3 |
(by the power rule) |
so the finished derivative is
| R ' |
= |
(1/2)*((-6)*q5 + 6)-1/2 ((-6)*5*q4 + 0) |
- |
4*q3 |
|
| |
= |
(-15)*q4 ((-6)*q5 + 6)-1/2 - 4*q3 |
![[]](/images/boxby.gif)
additional explanation for the derivative of sums
see another derivative of sums example
practice gateway test
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Comments to Gavin LaRose
glarose@umich.edu
©2001 Gavin LaRose,
University of Michigan Math Dept.