1）x²-4x+4=0
(x-2)²=0
x-2=0
x=2
(x+2)²=(2x-1)²
(x+2)²-(2x-1)²=0
(x+2+2x-1)(x+2-2x+1)=0
(3x+1)(-x+3)=0
3x+1=0 或 -x+3=0
x=-1/3 或 x=3
计算(1)（x²-49）÷（7-x)
=(x+7)(x-7)÷(7-x)
=-(x+7)
=-x-7
(2) (2ab²-8a²b²)÷(4a-b)
=2ab(b-4a)÷(4a-b)
=-2ab