解;
∫x(tanx)^2dx
=∫x[(secx)^2－1]dx
=∫x (secx)^2 dx－∫x dx
=∫x d(tanx) －x^2/2(下面用分步积分法)
=xtanx－∫tanxdx －x^2/2
=xtanx＋ln|cosx|－x^2/2＋C
(C是常数)