Posted by jj reddick on Friday, October 22, 2010 at 8:48pm.
make triangles for each case , then use Pythagoras
if sinx = 1/5, then cosx = √24/5
if cosy = 2/3 , the siny = √5/3
sin(x+y) = sinxcosy + cosxsiny
= (1/5)(2/3) + (√24/5)(√5/3)
= (2 + √120)/15
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