Express sin(x+y)

Answer 1

sin(x+y) = sinxcosy + sinycosx

it's one of the sum and difference formulas for sines

the other formula is

sin(x-y) = sinxcosy - sinycosx

then there're the sum and difference formulas for cosines

cos(x+y) = cosxcosy - sinxsiny

cos(x-y) = cosxcosy + sinxsiny