(x²+y²)(x²+y²-1)=12 x²+y²=

(x²+y²)(x²+y²-1)=12 x²+y²=

换元z = x²+y²,有z(z-1) = 12,即(z-4)(z+3) = 0.
x²+y² = z = -3或4.
但x,y为实数时,x²+y² ≥ 0,故x²+y² = 4.

吧X2+y2看成整体，即能得出结果是4