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
平方项与算术平方根均恒非负,三者之和=0,三者分别=0
x-2=0 x=2
y+3=0 y=-3
z+3=0 z=-3
(xy)^z=(2-3)^(-3)=(-1)^(-3)=-1