Single Choice

$$\displaystyle \int \frac {\sin^8 x-\cos^8 x}{(1-2\sin^2x \cos^2x)}dx$$ is equal is to

A$$\displaystyle \frac {1}{2}\sin 2x+c$$
B$$\displaystyle -\frac {1}{2}\sin 2x+c$$
C$$\displaystyle -\frac {1}{2}\sin x+c$$
Correct Answer
D$$\displaystyle-sin^2x+c$$

Solution

Given, $$\displaystyle\int { \frac { \sin ^{ 8 }{ x } -\cos ^{ 8 }{ x } }{ 1-2\sin ^{ 2 }{ x\cos ^{ 2 }{ x } } } dx }$$

$$=\displaystyle \int { \dfrac { (\sin ^{ 4 }{ x } -\cos ^{ 4 }{ x)(\sin ^{ 4 }{ x } +\cos ^{ 4 }{ x } ) } }{ 1-2\sin ^{ 2 }{ x\cos ^{ 2 }{ x } } } dx } $$

$$=\displaystyle \int { \dfrac { (\sin ^{ 4 }{ x } -\cos ^{ 4 }{ x)((\sin ^{2}{ x })^2+(\cos ^{2}{ x })^2 +2\sin^2x\cos^2x-2\sin^2x\cos^2x ) } }{ 1-2\sin ^{ 2 }{ x\cos ^{ 2 }{ x } } } dx } $$

$$=\displaystyle \int { \dfrac { (\sin ^{ 4 }{ x } -\cos ^{ 4 }{ x)((\sin ^{2}{ x }+\cos ^{2}{ x })^2 -2\sin^2x\cos^2x) } }{ 1-2\sin ^{ 2 }{ x\cos ^{ 2 }{ x } } } dx } $$

$$\displaystyle=\int { \dfrac { (\sin ^{ 2 }{ x } -\cos ^{ 2 }{ x)(1-2\sin ^{ 2 }{ x\cos ^{ 2 }{ x } } ) } }{ 1-2\sin ^{ 2 }{ x\cos ^{ 2 }{ x } } } dx } $$

$$=\displaystyle\int { (-\cos { 2x) } } dx=-\frac { \sin { 2x } }{ 2 } +C$$


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