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Provide solution for RD Sharma maths class 12 chapter 19 Definite Integrals exercise Multiple choice question 18

Answers (1)

Answer:

2

Given:

\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}} \sin |x| d x

Hint:

You must know about \left | x \right | function and \int \sin x\; dx
 

Explanation:  

Let

I=\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}} \sin |x| d x

We know that

\begin{aligned} &|x|=\left\{\begin{aligned} x, & x \geq 0 \\ -x, & x<0 \end{aligned}\right. \\\\ &I=\int_{-\frac{\pi}{2}}^{0} \sin (-x) d x+\int_{0}^{\frac{\pi}{2}} \sin x \; d x \end{aligned}

\begin{aligned} &I=-\int_{-\frac{\pi}{2}}^{0} \sin x \: d x+\int_{0}^{\frac{\pi}{2}} \sin x \; d x \\\\ &=-[-\cos x]_{-\frac{\pi}{2}}^{0}+[-\cos x]_{0}^{\frac{\pi}{2}} \end{aligned}

\begin{aligned} &=[\cos x]_{-\frac{\pi}{2}}^{0}-[\cos x]_{0}^{\frac{\pi}{2}} \\\\ &=\cos (0)-\cos \left(-\frac{\pi}{2}\right)-\cos \frac{\pi}{2}+\cos (0) \\\\ &=1-0-0+1 \\\\ &=2 \end{aligned}

 

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