设tanx=t,则x=arctant,sinx=t/√(t²+1),dx=dt/(t²+1)
于是,原式=∫[dt/(t²+1)]/[1+t²/(t²+1)]
=∫dt/(2t²+1)
=(1/√2)∫d(√2t)/[(√2t)²+1]
=(1/√2)arctan(√2t)+C (C是积分常数)
=(1/√2)arctan(√2tanx)+C.