Derivatives - Product Rule for Derivatives

Introduction

The product rule is a formula used to find the derivative of a function that is the product of two other functions.

Formula

If we have two functions, f(x) and g(x), then the product rule states: (f * g)' = f' * g + f * g'

Explanation

  • The derivative of the product of two functions is equal to the derivative of the first function times the second function plus the first function times the derivative of the second function.

Example 1

Find the derivative of the function f(x) = x^2 * sin(x). Step 1: Identify f(x) and g(x).

  • f(x) = x^2
  • g(x) = sin(x) Step 2: Find f’(x) and g’(x).
  • f’(x) = 2x
  • g’(x) = cos(x) Step 3: Apply the product rule formula. (f * g)' = f' * g + f * g' (x^2 * sin(x))' = (2x * sin(x)) + (x^2 * cos(x))

Example 2

Find the derivative of the function f(x) = e^x * ln(x). Step 1: Identify f(x) and g(x).

  • f(x) = e^x
  • g(x) = ln(x) Step 2: Find f’(x) and g’(x).
  • f’(x) = e^x
  • g’(x) = 1/x Step 3: Apply the product rule formula. (f * g)' = f' * g + f * g' (e^x * ln(x))' = (e^x * 1/x) + (e^x * ln(x))

Derivative Rules Reminder

  • The power rule: (x^n)' = nx^(n-1)
  • The constant rule: (c)' = 0
  • The sum rule: (f + g)' = f' + g'

Conclusion

The product rule allows us to find the derivative of a function that is the product of two other functions. By using the formula (f * g)' = f' * g + f * g', we can differentiate such functions efficiently and accurately.