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Provide solution for RD Sharma maths class 12 chapter Indefinite Integrals exercise 18.8 question 30

Answers (1)

Answer:

        \frac{1}{3}log\left | cos\, 3x \right |+C

Hint:

        U\! se\; cos\, A-cos\, B \: and\: sin\, A-sin\, B f\! ormula

Given:

        \int \! \frac{cos4x-cos2x}{sin4x-sin2x}dx

Explanation:

        \int \frac{-2 \sin \left(\frac{4 x-2 x}{2}\right) \sin \left(\frac{4 x+2 x}{2}\right)}{2 \cos \left(\frac{4 x+2 x}{2}\right) \sin \left(\frac{4 x-2 x}{2}\right)} d x \quad\left[\begin{array}{l} \cos A-\cos B=-2 \sin \left(\frac{A+B}{2}\right) \sin \left(\frac{A-B}{2}\right) \\ \sin A-\sin B=2 \cos \left(\frac{A+B}{2}\right) \sin \left(\frac{A-B}{2}\right) \end{array}\right]

        =-\int \! \frac{sin3x}{cos3x}dx

        =-\int \! \tan\, 3xdx

        =-[\frac{-log\left | cos\, 3x \right |}{3}]+C

        =\frac{1}{3}log\left | cos\, 3x \right |+C

Posted by

Gurleen Kaur

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