BITSAT 2010
- Exam
- BITSAT
- Year
- 2010
- Subject
- Mathematics
- Chapter
- Definite Integration
BITSAT 2010 · Mathematics · Definite Integration
(∫4 (x+(π)/(6)) 2 x · ((5 π)/(6)+ x) d x)
(\int4 \cos 2 x \cdot \cos \left(\frac{5 \pi}{6}+$x\right) d x)
Options
- A(-\left(x+\frac{\sin 4 x}{4}+\frac{\sin 2 x}{2}\right)+c)
- B(-\left(x+\frac{\sin 4 x}{4}-\frac{\sin 2 x}{2}\right)+c)
- C(-\left(x-\frac{\sin 4 x}{4}+\frac{\sin 2 x}{2}\right)+c)
- D(-\left(x-\frac{\sin 4 x}{4}+\frac{\cos 2 x}{2}\right)+c)
Correct answer
A. (-\left(x+\frac{\sin 4 x}{4}+\frac{\sin 2 x}{2}\right)+c)
Step-by-step solution
$\begin{aligned}& \int4 \cos \left( x+\frac{\pi}{6}\right) \cos2 x \cdot \cos \left(\frac{5 \pi}{6}+ x\right) d x \\
& =2 \int\left(\cos (2 x+\pi) \cos \frac{2 \pi}{3}\right) \cos2 x d x \\
& =2 \int\left(-\cos2 x-\frac{1}{2}\right) \cos2 x d x \\
& =\int\left(-2 \cos ^2 2 x-\cos 2 x\right) d x \\
& =-\int(1+\cos 4 x+\cos 2 x) d x \\
& =-x-\frac{\sin 4 x}{x}-\frac{\sin 2 x}{2}+ c
\end{aligned}$)