Problem now solved:

While Solve[ ] still fails to return an answer, Reduce[ ] does produce sensible output, if the argument is in entered using the "Basic Math Assistant Palette".

The original question was :

The attached problem - product of three matrices with sin(x) and cos(x) elements equals a matrix with y and z elements, find x, y and z - has a solution on Wolfram Alpha. As the two non-trivial solutions include many identical terms I would like to further simplify in Mathematica. After re-entering the problem in Mathematica Solve[ ] fails. Reduce[ ] appears to give an answer, but not in a useful (readable) format. In Wolfram Alpha the problem is

solve {{cos(x),-sin(x)},{sin(x),cos(x)}} {{A,B},{C,D}} {{cos(x),sin(x)},{-sin(x),cos(x)}}={{y,0},{0,z}}

A,B,C,D are positive real numbers and B=C.

Software used is Mathematica 7 on OS X 10.10.

Question: Is it possible to get a fully simplified answer in Mathematica?