@vv  ^_^ Fermart's last theorem!  Thanks, I now know I cannot trust all result it gives. 

Thanks to all of you, it really helps.

@Kitonum  I now know why I cannot assume gamma as positive yesterday. Thanks for your hint. ^_^

I remembered I did this by hand when I was in Middle school, but dunno how to do it on maple. 

@Carl Love  yes, you get it.^_^

@John Fredsted  Ha, I just want to show someone a propriety of this function f(w), if w1^2*w2^2=1, then we have f(w1)=f(w2). I put the variable at the denominator to make it easy to examine this point.

@Kitonum Thanks for clarification! I learned a lot. ^_^

@Kitonum   But what's the diffenrence between apply and ->?

@Carl Love 

@vv I followed your advice and it now works. Great!