Tích phân lượng giác

N

nguyenbahiep1

[laTEX]I = \int_{0}^{\frac{\pi}{2}}(1 -\frac{2(cosx-sinx)}{sinx+cosx+\sqrt{2}} - \frac{\sqrt{2}}{sinx+cosx+\sqrt{2}})dx \\ \\ I = \frac{\pi}{2}- 2ln|sinx+cosx+\sqrt{2}| \big|_{0}^{\frac{\pi}{2}} - I_1 \\ \\ I = \frac{\pi}{2} - I_1 \\ \\ I_1 = \int_{0}^{\frac{\pi}{2}}\frac{\sqrt{2}}{sinx+cosx+\sqrt{2}}dx \\ \\ I_1 = \int_{0}^{\frac{\pi}{2}}\frac{dx}{sin(x+\frac{\pi}{4})+1} \\ \\ x+\frac{\pi}{4} = 2t \\ \\ I_1 = \int_{\frac{\pi}{8}}^{\frac{3\pi}{8}}\frac{2dt}{1+sin2t} \\ \\ I_1 = \int_{\frac{\pi}{8}}^{\frac{3\pi}{8}}\frac{2dt}{(sint+cost)^2} \\ \\ I_1 = \int_{\frac{\pi}{8}}^{\frac{3\pi}{8}}\frac{dt}{cos^2(t-\frac{\pi}{4})} = tan(t-\frac{\pi}{4}) \big|_{\frac{\pi}{8}}^{\frac{3\pi}{8}}[/laTEX]
 
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