12x^2-5x-2=（3x^2-2）*（4x^2+1）
2x^2+4xy+2y^2-8z^2=2(x+y+2z)*(x+y-2z)
解方程：{x+y^2=6,y=x};
y=x
则
x+x^2-6=0
(x+3)*(x-2)=0
x=-3或x=2
x-12+根号x=0;
x=(12-x)^2
x=144+x^2-24x
x^2-25x+144=0
(x-16)*(x-9)=0
x=16或x=9
x^2 +3x+根号(x^2+3x)=6
设x^2+3x=t
则t+根号t=6
根号t=6-t
t=(6-t)^2
(t-4)*(t-9)=0
t=4或t=9
即x^2+3x=4或x^2+3x=9
x^2+3x=4时
（x+4）*（x-1）=0
x=1或x=-4
x^2+3x=9时
(x+3/2)^2=27/4
x=-3/2+3/2*根号3
或x=-3/2-3/2*根号3