Posted by Anonymous on Tuesday, February 21, 2012 at 3:31pm.
Simplify:
sin(xy)cosy+cos(xy)siny
= (sinxcosycosxsiny)cosy+(cosxcosy+sinxsiny)siny
= ???
What do I do next???
Please Help and Thank You

Trigonometry Help  Reiny, Tuesday, February 21, 2012 at 5:08pm
expand it again
= sinx cos^2 y  cosxsinycosy + cosxcosysiny + sinxsin^2 y
= sinx(cos^2 y  sin^2 y)
= sinxcos(2y) 
Trigonometry Help  Anonymous, Tuesday, February 21, 2012 at 5:19pm
when I substitue the x's and y's I get different answers.
do I need brackets on (sinxcosycosxsiny) and (cosxcosy+sinxsiny)?
could the next step be: sinxcosycosxsinycosy+cosxcosy+sinxsinysiny without the brackets? or would that be wrong? 
correction  Trigonometry Help  Reiny, Tuesday, February 21, 2012 at 6:01pm
found my error
2nd last line should have been
= sinx(cos^2 y + sin^2 y)
= sinx (1)
= sinx 
Trigonometry Help  Anonymous, Tuesday, February 21, 2012 at 6:12pm
thank you so much=)