y =x^2+2x. y=(-y)^2-2. y^2-y-2=0
<=>. <=>.
y-x= 0. x=-y. x=-y
| y^2-y-2=0
| D = 1+4*2= 9
|y1/y2 = 1±3/2
|y1 = 2 , y2 = -1
y1 = 2, y2 = -1
x1 = -2, x2 = 1
