Question

Проинтегрировать тригонометрическое выражение: dx/(sin2x+cos2x)

Answer 1

$\int \frac{dx}{sin2x+cos2x}=[\, t=tgx,\; sin2x=\frac{2t}{1+t^2},cos2x=\frac{1-t^2}{1+t^2},\\\\x=arctgt,\; dx=\frac{dt}{1+t^2}\, ]=\int \frac{\frac{dt}{1+t^2}}{\frac{2t}{1+t^2}+\frac{1-t^2}{1+t^2}}=\int \frac{dt}{-(t^2-2t-1)}=\\\\=-\int \frac{dt}{(t-1)^2-2} =[\, u=t-1,\; t=u+1,\; du=dt\, ]=\\\\=-\int \frac{du}{u^2-2}=-\frac{1}{2\sqrt2}\cdot ln\left |\frac{u-\sqrt2}{u+\sqrt2}\right |+C=-\frac{1}{2\sqrt2}\cdot ln\left |\frac{tgx-1-\sqrt2}{tgx-1+\sqrt2}\right |+C$