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Provide Solution For R.D. Sharma Maths Class 12 Chapter 18  Indefinite Integrals Exercise  Revision Exercise Question 78 Maths Textbook Solution.

Answers (1)

Answer:

\ln |\sec x+\tan x|-\sin x-\frac{\sin 3 x}{3}-\frac{\sin ^{5} x}{5}+c

Hint:

To solve the given equation we have to split the sin? x term in sin? x.sin² x.

Given:

\int \frac{\sin ^{6} x}{\cos x} d x

Solution:

I=\int \frac{\sin ^{6} x}{\cos x} d x

   =\int \frac{\sin ^{4} x \sin ^{2} x}{\cos x} d x=\int \frac{\sin ^{4} x}{\cos x}\left(1-\cos ^{2} x\right) d x

 =\int \frac{\sin ^{4} x}{\cos x} d x-\int \frac{\sin ^{4} x \cos ^{2} x}{\cos x} d x

  =\int \frac{\sin ^{4} x}{\cos x} d x-\int \sin ^{4} x \cos x d x

=\int \frac{\sin ^{2} x\left(1-\cos ^{2} x\right)}{\cos x} d x-\int t^{4} d t

 =\int \frac{\sin ^{2} x}{\cos x} d x-\int \sin ^{2} x \cos x d x-\frac{t^{5}}{5}

=\int \frac{\left(1-\cos ^{2} x\right)}{\cos x} d x-\int t^{2} d t-\frac{\sin ^{5} x}{5}

=\int \frac{1}{\cos x} d x-\int \cos x d x-\frac{t^{8}}{3}-\frac{\sin ^{5} x}{5}

=\int \sec x d x-\sin x-\frac{\sin 3 x}{3}-\frac{\sin ^{5} x}{5}

=\ln |\sec x+\tan x|+\left(-\sin x-\frac{\sin 3 x}{3}-\frac{\sin ^{5} x}{5}\right)+c

=\ln |\sec x+\tan x|-\sin x-\frac{\sin 3 x}{3}-\frac{\sin ^{5} x}{5}+c

 

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