y·sinx = cos(x-y)
[y·sinx ]' = [cos(x-y)]'
y'·sinx + y·cosx = -sin(x-y)·(1-y')
y'·sinx + y·cosx = -sin(x-y)+sin(x-y)·y'
sin(x-y)·y' - y'·sinx = y·cosx + sin(x-y)
y'·(sin(x-y) - sinx) = y·cosx + sin(x-y)
y·sinx = cos(x-y)
[y·sinx ]' = [cos(x-y)]'
y'·sinx + y·cosx = -sin(x-y)·(1-y')
y'·sinx + y·cosx = -sin(x-y)+sin(x-y)·y'
sin(x-y)·y' - y'·sinx = y·cosx + sin(x-y)
y'·(sin(x-y) - sinx) = y·cosx + sin(x-y)