HELP FAST PLEASE!!!Show that sin(x+pi)=-sinx

sin(a + b) = sin(a)cos(b) + sin(b)cos(a)
sin(x + pi) = sin(x)cos(pi) + cos(x)sin(pi)

sin(pi) = 0cos(pi) = -1

sin(x + pi) = sin(x)(-1) + cos(x)(0)
sin(x + pi) = -sin(x) + 0