x²+5x+2=0 -> x²+5x+25/4=17/4,所得方程为(x+5/2)²=17/4
3x²-4x-2=0 -> 3(x²-4x/3)=2,3(x²-4x/3+4/9)=10/3,所得方程为(x-2/3)²=10/9