楼上错了
2x²-5x-1=0
2x²-5x=1
x²-5/2x=1/2
x²-5/2x+(5/4)²=1/2+(5/4)²
(x-5/4)²=8/16+25/16
x-5/4=±√33/4
x=5/4±√33/4