# If ∫ Sin 8 X − Cos 8 X 1 − 2 Sin 2 X Cos 2 X D X - Mathematics

MCQ

If $\int\frac{\sin^8 x - \cos^8 x}{1 - 2 \sin^2 x \cos^2 x} dx$

• -1/2

• 1/2

• -1

• 1

#### Solution

−1/2

$\text{If }\int\left( \frac{\sin^8 x - \cos^8 x}{1 - 2 \sin^2 x \cos^2 x} \right)dx = a \sin 2x + C ..............(1)$

$\text{Considering LHS of eq. (1)}$

$\Rightarrow \int\frac{\left( \sin^4 x - \cos^4 x \right) \left( \sin^4 x + \cos^4 x \right)}{\left( 1 - 2 \sin^2 x \cos^2 x \right)}$

$\Rightarrow \int\frac{\left( \sin^2 x - \cos^2 x \right) \left( \sin^2 x + \cos^2 x \right) \cdot \left( \sin^4 x + \cos^4 x \right) dx}{\left\{ \left( \sin^2 x + \cos^2 x \right)^2 - 2 \sin^2 x \cos^2 x \right\}}$

$\Rightarrow \int\frac{\left( \sin^2 x - \cos^2 x \right) \cdot \left( \sin^4 x + \cos^4 x \right)dx}{\left( \sin^4 x + \cos^4 x + 2 \sin^2 x \cos^2 x - 2 \sin^2 x \cos^2 x \right)}$

$\Rightarrow - \int\frac{\left( \cos^2 x - \sin^2 x \right) \times \left( \sin^4 x + \cos^4 x \right) dx}{\left( \sin^4 x + \cos^4 x \right)}$

$\Rightarrow - \int\cos \left( 2x \right) dx ..............\left( \because \cos^2 x - \sin^2 x = \cos 2x \right) .............(2)$

$\text{Comparing the RHS of eq. (1) with eq. (2) we get,}$

$a = - \frac{1}{2}$

Concept: Indefinite Integral Problems
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#### APPEARS IN

RD Sharma Class 12 Maths
Chapter 19 Indefinite Integrals
MCQ | Q 8 | Page 200