- Difficulty
- Standard
- Suggested time
- 3 min
- Marks
- 2
Implicit differentiation and inverse trigonometric functions practice question 10
Given , which expression is ?
appears on both sides of the equation, once inside a sine. When you differentiate with respect to , what does every term built from pick up?
Differentiating with respect to gives , not .
Gather both terms on one side and factor.
Theory UBC Math 100 §4.5CLP-1 §2.11Key results
Worked solution
Strategy
Differentiate each side with respect to x, letting the chain rule attach dy/dx to every term built from y, then isolate dy/dx.
Working
Both sin(y) and the bare y on the right produce a dy/dx factor.
Move the dy/dx terms to the same side.
Factor dy/dx out of both terms.
Divide by the bracket.
Answer
The answer is 2x/(1 − cos y).
Check
With the curve written as x² = y − sin y, differentiating in y gives 2x · dx/dy = 1 − cos y, and flipping dx/dy gives 2x/(1 − cos y).
Where this goes wrong
Differentiating sin(y) as cos(y) and forgetting dy/dx, which leaves nothing to solve for. Every function of y contributes a dy/dx factor when you differentiate with respect to x.
Leans on
Chain rule with an unknown inner function, from The chain rule and logarithms
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