[[cos(b),0,sin(b)],[0,1,0],[-sin(b),0,cos(b)]]*[[cos(a), sin(a), 0],[-sin(a), cos(a), 0],[0,0,1]]

Uh oh! Wolfram|Alpha doesn't run without JavaScript.

Please enable JavaScript. If you don't know how, you can find instructionshere.Once you've done that, refresh this page to start using Wolfram|Alpha.