int_{-frac{pi}{2}}^{frac{pi}{2}} left(x^2 + l | vedclass

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Question

(C) Let $I = \int_{-\frac{\pi}{2}}^{\frac{\pi}{2}} \left(x^2 + \log \left(\frac{\pi-x}{\pi+x}\right) \cdot \cos x\right) dx$. Split the integral into

Vedclass · Accepted Answer

$\frac{\pi^3}{12}$

Vedclass · Answer

(C) Let $I = \int_{-\frac{\pi}{2}}^{\frac{\pi}{2}} \left(x^2 + \log \left(\frac{\pi-x}{\pi+x}\right) \cdot \cos x\right) dx$. Split the integral into two parts: $I = \int_{-\frac{\pi}{2}}^{\frac{\pi}{2}} x^2 dx + \int_{-\frac{\pi}{2}}^{\frac{\pi}{2}} \log \left(\frac{\pi-x}{\pi+x}\right) \cdot \cos x dx$. Let $f(x) = \log \left(\frac{\pi-x}{\pi+x}\right) \cdot \cos x$. Then $f(-x) = \log \left(\frac{\pi-(-x)}{\pi+(-x)}\right) \cdot \cos(-x) = \log \left(\frac{\pi+x}{\pi-x}\right) \cdot \cos x = \log \left(\left(\frac{\pi-x}{\pi+x}\right)^{-1}\right) \cdot \cos x = -\log \left(\frac{\pi-x}{\pi+x}\right) \cdot \cos x = -f(x)$. Since $f(x)$ is an odd function,$\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}} f(x) dx = 0$. Thus,$I = \int_{-\frac{\pi}{2}}^{\frac{\pi}{2}} x^2 dx = 2 \int_{0}^{\frac{\pi}{2}} x^2 dx = 2 \left[ \frac{x^3}{3} \right]_{0}^{\frac{\pi}{2}} = 2 \cdot \frac{(\pi/2)^3}{3} = 2 \cdot \frac{\pi^3}{8 \cdot 3} = \frac{\pi^3}{12}$.

$\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}} \left(x^2 + \log \left(\frac{\pi-x}{\pi+x}\right) \cdot \cos x\right) dx =$

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