Question

Решите интеграл: dx/(sin^2 (x)*(1+cos (x))

Answer 1

$\int \frac{dx}{sin^2x(1+cosx)} =[\; t=tg \frac{x}{2}\; ,\; sinx= \frac{2t}{1+t^2}\; ,\; cosx= \frac{1-t^2}{1+t^2}\; ,\\\\dx= \frac{2\, dt}{1+t^2} \; ]=\int \frac{2\, dt}{(1+t^2)\cdot \frac{4t^2}{(1+t^2)^2}\cdot (1+\frac{1-t^2}{1+t^2} )} =\int \frac{2\, dt}{\frac{4t^2}{1+t^2}\cdot \frac{1+t^2+1-t^2}{1+t^2} } =\\\\=\int \frac{(1+t^2)^2\, dt}{2t^2\cdot 2} = \frac{1}{4}\cdot \int \frac{1+2t^2+t^4}{t^2} dt= \frac{1}{4}\cdot \int (t^{-2}+2+t^2)dt=$

$= \frac{1}{4}\cdot \Big (\frac{t^{-1}}{-1}+2t+\frac{t^3}{3})= \frac{1}{4}\cdot (-\frac{1}{tg\frac{x}{2}}+2\, tg \frac{x}{2} + \frac{1}{3}\, tg^3\, \frac{x}{2})+C$