Chain Rule - Calculus I - Lecture Slides, Slides of Calculus

In my class of Calculus-I, I take lecture note from these slides, hope these lecture slides help other student.The key point in these slides are:Chain Rule, Composite Function, Leibniz Notation, Differentiable Functions, Outer Function, Derivative of Function, Power Rule, Real Number, Implicit Differentiation, Variable Explicitly, Equation of Tangent Line

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2012/2013

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2.5 The Chain Rule
If 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 =
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2.5 The Chain Rule

If 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

F ′( x) = f ′(g(x))⋅ g′(x )

dx

du

du

dy

dx

dy

Example:

( (^ )) ( )

2 f g x = sin x − 4

( )

2 y = sin x − 4

y = sinu

2 u = x − 4

cos

dy u du

= 2

du x dx

=

dy dy du

dx du dx

= ⋅

cos 2

dy u x dx

= ⋅

( )

2 cos 4 2

dy x x dx

= − ⋅

( )

2 y = sin x − 4

( ) ( )

2 2 cos 4 4

d y x x dx

′ = − ⋅ −

( )

2 y ′ = cos x − 4 ⋅ 2 x

A faster way to write the solution:

Differentiate the outer function...

…then the inner function

Another example:

( )

2 cos 3

d x dx

( )

2 cos 3

d x dx

2 cos 3 ( ) cos 3( )

d x x dx

 ^ ⋅

2 cos 3 ( ) sin 3( ) ( 3 )

d x x x dx

−2 cos 3 (^) ( x (^) ) ⋅ sin 3( x)⋅ 3

−6 cos 3 ( x (^) ) sin 3( 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

d n n 1 du

u nu

dx dx

[ ( )] [ ( )] ( )

1 g x n g x g x dx

d (^) n n = ⋅ ′

If n is any real number and u=g(x) is differentiable,

then

Alternatively,

Example:

[ ( ) ] ( ) ( )

2 50 2 49

2 50 2 49 2

50 3 2 100 3

3 50 3 3

= − ⋅ = −

− = − −

x x x x

x dx

d x x dx

d

2 2 x + y = 1

This is not a function,

but it would still be

nice to be able to find

the slope.

2 2 1

d d d x y dx dx dx

  • = Do the same thing to both sides.

2 2 0

dy x y dx

  • =

Note use of chain rule.

2 2

dy y x dx

= −

2

2

dy x

dx y

dy x

dx y

= −

Example 1:

2 2 y = x +sin y

2 2 sin

d d d y x y dx dx dx

= +

This can’t be solved for y.

2 2 cos

dy dy x y dx dx

= +

2 cos 2

dy dy y x dx dx

− =

( 2 cos ) 2

dy y x dx

− =

2

2 cos

dy x

dx y

= −

Example 2:

Higher Order Derivatives

Find if.

2

2

d y

dx

3 2 2 x − 3 y = 7

3 2 2 x − 3 y = 7

2 6 x − 6 y y′ = 0

2 − 6 y y ′ = − 6 x

2 6

x y y

2 x y y

2

2

y 2 x x y y y

⋅ −^ ′

2

2

2 x x y y y y

2 2

2

2 x x y y

x

y y

4

3

2 x x y y y

Substitute

back into the

equation.

y′