1.已知x.y满足x^2+y^2-4x-6y+13=0,
（x-2)^2+(y-3)^2=0
x=2,y=3
(-y/x^3)^3除以(-1/xy)^4乘(x/y^2)^2
=(-3/2^3)^3÷（-1/2×3）^4×（2/3^2)^2
=-3^3/2^9×6^4×2^2/3^4
2.已知x^2+1/x=4.求x^2+1/x^2的值