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Derivatives & Second-Order Derivatives · Question 35 of 96

Question 35

MediumOriginal question

If x=sin⁡yx = \sin y, what is dydx\frac{dy}{dx} in terms of xx?

Options for question 35

Show the answer and explanation
CorrectNot quiteAnswer D

Correct answer: D

Explanation

  1. Differentiate with respect to xx: 1=cos⁡ydydx1 = \cos y\frac{dy}{dx}, so dydx=1cos⁡y\frac{dy}{dx} = \frac{1}{\cos y}.

  2. cos⁡y=1−sin⁡2y=1−x2\cos y = \sqrt{1 - \sin^2 y} = \sqrt{1 - x^2} (taking cos⁡y>0\cos y > 0), so dydx=11−x2\frac{dy}{dx} = \frac{1}{\sqrt{1 - x^2}}.

Worth noting

1cos⁡x\frac{1}{\cos x} puts xx where yy belongs: the derivative is 1cos⁡y\frac{1}{\cos y}, rewritten with sin⁡y=x\sin y = x.

Concept
Writing an implicit derivative in terms of x
Typical time
90 s
Your time
—
The rule this testsImplicit functions
Practise this chapter →

Ten questions from Derivatives & Second-Order Derivatives, at your own pace.

Practise this chapter →

Ten questions from Derivatives & Second-Order Derivatives, at your own pace.