用凑微分法解答tan(x+3)/cos^2(x+3) dx
问题描述：
用凑微分法解答tan(x+3)/cos^2(x+3) dx
tan(x+3)/[cos(x+3)]^2 dx
答
∫tan(x+3)/[cos(x+3)]^2 dx
=∫sin(x+3)/[cos(x+3)]^3 dx
=-∫ [cos(x+3)]^(-3) dcos(x+3) 这样就凑好了答案是什么呢令t=cos(x+3)原式=-∫ t^(-3) dt 这个会做了吧，最好把t=cos(x)代回，就好也=t^(-2)/2 + C=(1/2)(cos(x+3)]^(-2) + C