Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Indefinite Integration

Question:

The value of $\int\frac{dx}{\sin^6x}$ is:

Options:

$-\frac{\cot^5x}{5}-2\frac{\cot^3x}{3}-\cot x +C$

$\frac{\cot^5x}{5}+2\frac{\cot^3x}{3}-\cot x +C$

$-\frac{\cot^3x}{5}-2\frac{\cot^5x}{3}-\cot x +C$

None of these

Correct Answer:

$-\frac{\cot^5x}{5}-2\frac{\cot^3x}{3}-\cot x +C$

Explanation:

$I=\int\frac{dx}{\sin^6x}=\int cosec^4x.cosec^2x\, dx$ [Put cot x - t ⇒ -cosec2x dx = dt]

$=\int(\cot^2x+1)^2cosec^2x\,dx=\int(t^2+1)^2(-dt)=-\frac{t^5}{5}-2\frac{t^3}{3}-t+C$  (where t = cot x)