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Implicit Differentiation

David Brown

David Brown

7 min read

Study Guide Overview

This guide covers implicit functions and implicit differentiation. It explains how to differentiate equations involving both x and y using the chain rule, product rule, and quotient rule. It includes examples of finding derivatives at specific points and differentiating inverse functions implicitly. Practice questions and a glossary are also provided.

#Derivatives of Implicit Functions

#Table of Contents

  1. Introduction to Implicit Functions
  2. Implicit Differentiation
  3. Examples and Applications
  4. Differentiating Inverse Functions
  5. Practice Questions
  6. Glossary
  7. Summary and Key Takeaways

#Introduction to Implicit Functions

#What is an Implicit Function?

  • An equation in the form y=f(x)y=f(x)y=f(x) or x=f(y)x=f(y)x=f(y) is written explicitly.
Exam Tip

E.g. y=3x2+2x−3y=3x^2 + 2x - 3y=3x2+2x−3

  • Equations involving both xxx and yyy are referred to as implicit functions.
Exam Tip

E.g. 3x^2 - 7xy^2 = 3 or x2+y2=25x^2 + y^2 = 25x2+y2=25

  • For such equations, we cannot express yyy solely in terms of xxx or vice versa.
  • However, these equations define a relationship between xxx and yyy.

#Implicit Differentiation

#What is Implicit Differentiation?

  • Implicit differentiation is the method used to differentiate implicit functions.
  • To differentiate an implicit function with respect to xxx, each term is differentiated with respect to xxx.
  • For terms involving only xxx, this is straightforward.
  • For terms involving yyy, we apply the chain rule.
Key Concept

ddxf(y)=f′(y)⋅dydx\frac{d}{dx}f(y) = f'(y) \cdot \frac{dy}{dx}dxd​f(y)=f′(y)⋅dxdy​ This means:

  • Differentiate the function in terms of yyy with respect to yyy.
  • Multiply it by dydx\frac{dy}{dx}dxdy​.
  • Once each term has been differentiated, rearrange the equation to solve for dydx\frac{dy}{dx}dxdy​.
  • Factorize out dydx\frac{dy}{dx}dxdy​ if necessary.
  • Substitute specific (x,y)(x, y)(x,y) values to find the derivative at a point if required.

#How to Use Implicit Differentiation?

#Example

Differentiate $x^2 + y^2 =...

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Question 1 of 8

Which of the following equations represents an implicit function? 🤔

y=5x3−2x+1y = 5x^3 - 2x + 1y=5x3−2x+1

x=2y2+3y−4x = 2y^2 + 3y - 4x=2y2+3y−4

x2+y2=16x^2 + y^2 = 16x2+y2=16

f(x)=4x−7f(x) = 4x - 7f(x)=4x−7