The Chain Rule: Fresh Take

  • Explain and use the chain rule
  • Use the chain rule along with other rules to differentiate functions involving powers, products, quotients, and trigonometry
  • Use the chain rule to find derivatives when multiple functions are nested together

Deriving the Chain Rule

The Main Idea 

  • Chain Rule Definition:
    • For h(x)=f(g(x)), the derivative is: h(x)=f(g(x))g(x)
  • Alternative Notation:
    • If y is a function of u, and u is a function of x: dydx=dydududx
  • Purpose:
    • Simplifies differentiation of composite functions
    • Breaks down complex functions into simpler parts
  • Useful for functions like sin(x3) or 3x2+1
  • Chain rule can be applied iteratively for functions with multiple compositions

Differentiate h(x)=esin(x2) using the chain rule.

Combining the Chain Rule With Other Rules

The Main Idea 

  • Chain Rule with Power Rule:
    • For h(x)=(g(x))n, the derivative is: h(x)=n(g(x))n1g(x)
  • Chain Rule with Trigonometric Functions:
    • Example: ddx(sin(g(x)))=cos(g(x))g(x)
  • Chain Rule with Product Rule:
    • Apply product rule first, then chain rule to each term
  • General Strategy:
    • Identify the composition of functions
    • Apply appropriate rules in the correct order
    • Simplify the result

Find the derivative of h(x)=(2x3+2x1)4

Find the equation of the line tangent to the graph of f(x)=(x22)3 at x=2.

Find the derivative of h(x)=sin(7x+2).

Find the derivative of h(x)=x(2x+3)3

Applying the Chain Rule Multiple Times

The Main Idea 

  • Chain Rule for Composition of Three Functions:
    • For k(x)=h(f(g(x))), the derivative is: k(x)=h(f(g(x)))f(g(x))g(x)
  • General Approach:
    • Work from the outside in
    • Apply the chain rule as many times as necessary
  • Number of Terms:
    • The derivative of a composition of n functions will have n terms

Find the derivative of h(x)=sin6(x3)

A particle moves along a coordinate axis. Its position at time t is given by s(t)=sin(4t). Find its acceleration at time t.

Let h(x)=f(g(x)). If g(2)=3,g(2)=4, and f(3)=7, find h(2).

Find the derivative of y=ln(sin(e2x)).

The Chain Rule Using Leibniz’s Notation

The Main Idea 

  • Leibniz’s Notation for Chain Rule:
    • For y=f(u) and u=g(x), the chain rule is expressed as: dydx=dydududx
  • Interpretation:
    • dydx: Rate of change of y with respect to x
    • dydu: Rate of change of y with respect to u
    • dudx: Rate of change of u with respect to x
  • Advantages:
    • Provides a clear visual representation of the chain rule
    • Helps in understanding the relationship between variables

Use Leibniz’s notation to find the derivative of y=cos(x3). Make sure that the final answer is expressed entirely in terms of the variable x.

Find the derivative of y=sin(2x3) using Leibniz’s notation.