x²-4x+y²+6y+√(z-3)+13=0
x²-4x+4+y²+6y+9+√(z-3)=0
(x-2)²+(y+3)²+√(z-3)=0
因此x=2,y=-3,z=3
(xy)^z = (2*(-3))^3 = -216