1.x（x-1）=x
x²-x=x
x-2x=0
x(x-2)=0
x=0或x=2
2.x²-6x+9=（5-2x）
x²-6x+9=5-2x
x²-4x+4=0
(x-2)²=0
x=2
3.x²-2x-1=0
x²-2x=1
(x-1)²=2
x-1=±√2
x=1+√2或x=1-√2
4.2x²-5x-7=0
(2x-7)(x+1)=0
x=7/2或x=-1