d^(2)z/dx^2=(e^(x-3y)*sin(x+3y)+e^(x-3y)*cos(x+3y))'=
=(x-3y)'e^(x-3y)*(-cos(x+3y)(x+3y)')+e^(x-3y)*(x-3y)'*sin(x+3y)*(x+3y)'=
=-e^(x-3y)*cos(x+3y)+e^(x-3y)*sin(x+3y)

верно нашла?