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∫04πx1+∣cos⁡x∣dx=\int_0^{4\pi} \frac{x}{1 + |\cos x|} dx =

Solution

✅ Correct Option: 2

Let I=∫04πx1+∣cos⁡x∣dxI = \int_0^{4\pi} \frac{x}{1+|\cos x|} dx. Using ∫0af(x)dx=∫0af(a−x)dx\int_0^a f(x)dx = \int_0^a f(a-x)dx: I=∫04π4π−x1+∣cos⁡x∣dxI = \int_0^{4\pi} \frac{4\pi - x}{1+|\cos x|} dx. Adding: 2I=4π∫04πdx1+∣cos⁡x∣2I = 4\pi \int_0^{4\pi} \frac{dx}{1+|\cos x|}. Since ∣cos⁡x∣|\cos x| has period π\pi, ∫04π=4∫0π=4⋅2=8\int_0^{4\pi} = 4 \int_0^{\pi} = 4 \cdot 2 = 8. So 2I=32π2I = 32\pi, giving I=16πI = 16\pi.

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