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Indefinite Integrals · Question 14 of 90

Question 14

MediumOriginal question

Evaluate ∫sin⁡xcos⁡2x dx\int \frac{\sin x}{\cos^{2} x}\,dx.

Options for question 14

Show the answer and explanation
CorrectNot quiteAnswer B

Correct answer: B

Explanation

  1. sin⁡xcos⁡2x=1cos⁡x⋅sin⁡xcos⁡x=sec⁡xtan⁡x\frac{\sin x}{\cos^{2} x} = \frac{1}{\cos x} \cdot \frac{\sin x}{\cos x} = \sec x\tan x.

  2. ∫sec⁡xtan⁡x dx=sec⁡x+C\int \sec x\tan x\,dx = \sec x + C.

Worth noting

−sec⁡x-\sec x gets the sign wrong: ddxsec⁡x=+sec⁡xtan⁡x\frac{d}{dx}\sec x = +\sec x\tan x.

Concept
Standard trigonometric integrals
Typical time
90 s
Your time
—
The rule this testsIntegration as the reverse of differentiation
Practise this chapter →

Ten questions from Indefinite Integrals, at your own pace.

Practise this chapter →

Ten questions from Indefinite Integrals, at your own pace.