Gujarat BoardEnglish MediumSTD 12 ScienceMathsIntegrals2 Marks
Question
Find the integral of the function sin3 x cos3 x
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Answer
Let $I=\int \sin ^{3} x \cos ^{3} x \cdot d x$ $\Rightarrow \int \cos ^{3} x \cdot \sin ^{2} x \cdot \sin x \cdot d x$ $\Rightarrow \int \cos ^{3} x\left(1-\cos ^{2} x\right) \sin x \cdot d x$ Let cos x = t $\Rightarrow$ -sinx.dx = dt $\Rightarrow \mathrm{I}=-\int \mathrm{t}^{3}\left(1-\mathrm{t}^{2}\right) \mathrm{dt}$ $=-\int\left(t^{3}-t^{5}\right) d t$ $=-\left\{\frac{t^{4}}{4}-\frac{t^{6}}{6}\right\}+C$ $=-\left\{\frac{\cos ^{4} x}{4}-\frac{\cos ^{6} x}{6}\right\}+C$ $=\frac{\cos ^{6} x}{6}-\frac{\cos ^{4} x}{4}+C$
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