2x^2-x{x+2}=x-1
2x^2－x^2－2X-X+1 = 0
x^2－3X+1 ＝ 0
X = ( 3 ±√[(-3)^2 - 4×1] ) / 4
∴ X1=( 3 +√5) / 4
X2 =( 3 -√5 )/ 4