2.4 the chain rule if f and g are both differentiable and f is the composite function defined by...
TRANSCRIPT
2.4 The Chain RuleIf f and g are both differentiable and F is the composite function defined by F(x)=f(g(x)), then F is differentiable and F′ is given by the product
In Leibniz notation, if y=f(u) and u=g(x) are both differentiable functions, then
)())(()( xgxgfxF
dx
du
du
dy
dx
dy
Example:
2sin 4f g x x
2sin 4y x
siny u 2 4u x
cosdy
udu
2du
xdx
dy dy du
dx du dx
cos 2dy
u xdx
2cos 4 2dy
x xdx
2sin 4y x
2 2cos 4 4d
y x xdx
2cos 4 2y x x
A faster way to write the solution:
Differentiate the outer function...
…then the inner function
Another example:
2cos 3d
xdx
2cos 3
dx
dx
2 cos 3 cos 3d
x xdx
derivative of theouter function
derivative of theinner function
It looks like we need to use the chain rule again!
Another example:
2cos 3d
xdx
2cos 3
dx
dx
2 cos 3 cos 3d
x xdx
2cos 3 sin 3 3d
x x xdx
2cos 3 sin 3 3x x
6cos 3 sin 3x x
The chain rule can be used more than once.
(That’s what makes the “chain” in the “chain rule”!)
The Power Rule combined with the Chain Rule
1n nd duu nu
dx dx
)()()( 1 xgxgnxgdx
d nn
If n is any real number and u=g(x) is differentiable, then
Alternatively,
Example:
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xxxx
xdx
dxx
dx
d