Rút gọn M = sin(x – y)cosy + cos(x – y)siny.
Giải thích
sin(x–y) cosy + cos(x–y) siny
= (sinx.cosy – cosx.siny).cosy + (cosx.cosy + sinx.siny).siny
= sinx .(cos²y + sin2y)
= sinx.
sin(x–y) cosy + cos(x–y) siny
= (sinx.cosy – cosx.siny).cosy + (cosx.cosy + sinx.siny).siny
= sinx .(cos²y + sin2y)
= sinx.