已知x^2-18x+m=（x+n）^2,则m分之n= 已知(x^2+y^2)(x^2-1+y^2)-12=0求x^2+y^2的值.
问题描述：
已知x^2-18x+m=（x+n）^2,则m分之n= 已知(x^2+y^2)(x^2-1+y^2)-12=0求x^2+y^2的值.
答
1.x^2-18x+m = x^2 +2nx + n^2
2n = -18,n = -9
m = n^2 = 81
n/m = -9/81 = -1/9
2.设x^2+y^2 = a,a(a-1) -12 = 0,a^2 -a -12 = 0
(a-4)(a+3) = 0
a = 4 (a = -3 x^2+y^2 = 4