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Q.Find the integral: ∫ex(1+sin⁡x1+cos⁡x)dx\displaystyle\int e^x \left(\dfrac{1+\sin x}{1+\cos x}\right) dx

(OR)
Evaluate ∫0πlog⁡(1+cos⁡x) dx\displaystyle\int_0^{\pi} \log(1+\cos x)\, dx.
Uttarakhand UbseUttarakhand Board Intermediate (Class 12) 2024Subjective· 4mImportance★★★★★
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Part 1: rewrite the integrand using half-angle identities as f(x)+f′(x)f(x)+f'(x) with f(x)=tan⁡(x/2)f(x)=\tan(x/2), then apply ∫ex[f(x)+f′(x)]dx=exf(x)+C\int e^x[f(x)+f'(x)]dx=e^xf(x)+C. Part 2 (OR): use 1+cos⁡x=2cos⁡2(x/2)1+\cos x=2\cos^2(x/2) and the known result ∫0π/2log⁡cos⁡t dt=−π2log⁡2\int_0^{\pi/2}\log\cos t\,dt=-\frac\pi2\log2.

Part 1: ∫ex(1+sin⁡x1+cos⁡x)dx\displaystyle\int e^x\left(\frac{1+\sin x}{1+\cos x}\right)dx

Using half-angle identities 1+cos⁡x=2cos⁡2(x/2)1+\cos x = 2\cos^2(x/2) and sin⁡x=2sin⁡(x/2)cos⁡(x/2)\sin x = 2\sin(x/2)\cos(x/2):

1+sin⁡x1+cos⁡x=1+2sin⁡(x/2)cos⁡(x/2)2cos⁡2(x/2)=12cos⁡2(x/2)+sin⁡(x/2)cos⁡(x/2)=12sec⁡2(x2)+tan⁡(x2)\frac{1+\sin x}{1+\cos x} = \frac{1+2\sin(x/2)\cos(x/2)}{2\cos^2(x/2)} = \frac{1}{2\cos^2(x/2)} + \frac{\sin(x/2)}{\cos(x/2)} = \frac12\sec^2\left(\frac x2\right) + \tan\left(\frac x2\right)

Let f(x)=tan⁡(x/2)f(x)=\tan(x/2). Then f′(x)=12sec⁡2(x/2)f'(x) = \dfrac12\sec^2(x/2). So the integrand is exactly f(x)+f′(x)f(x)+f'(x).

Using the standard result ∫ex[f(x)+f′(x)] dx=exf(x)+C\displaystyle\int e^x[f(x)+f'(x)]\,dx = e^xf(x)+C:

∫ex(1+sin⁡x1+cos⁡x)dx=extan⁡(x2)+C\int e^x\left(\frac{1+\sin x}{1+\cos x}\right)dx = e^x\tan\left(\frac x2\right) + C


OR: I=∫0πlog⁡(1+cos⁡x) dx\displaystyle I=\int_0^\pi \log(1+\cos x)\,dx

Using 1+cos⁡x=2cos⁡2(x/2)1+\cos x = 2\cos^2(x/2): …

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