precalc and trig
posted by hayden .
cos^2 (a+x) sin^2 a=cos x * cos(2a+x)

see
http://www.jiskha.com/display.cgi?id=1235346549
don't tell my I did all that work, and you didn't even look at it. 
i posted a sorry. i posted this twice on that one. And i don't understand how RS=LS and thanks