有两个实数根
x²-3x-a²-a+2=0
x²-3x-a²-a+9/4-1/4=0
x²-3x+9/4-a²-a-1/4=0
(x²-3x+9/4)-(a²+a+1/4)=0
(x-3/2)²-(a+1/2)²=0
(x-3/2)²=(a+1/2)²
x-3/2=±(a+1/2)
x=3/2±(a+1/2)
x1=2+a
x2=1-a