I have been working on this integration problem for awhile now and am completely stuck: Integral of tanx*tan2x*tan3x I know I am suppose to use substituion and for that matter probably multiple substitions. But I am no sure what I should use for my first value of "u". I have changed the problem to be in terms of sin and cos, but I am still just ending up at a dead end. If some one can help me start off in the right step I would greatly appreciatte it. I DO NOT want the answer, I would like to solve it for myself, I just need help starting it off right. Thanks in advance.