120x-120(x-2)=3x(x-2)
即：40x-40(x-2)=x(x-2)
40x-40x+80=x²-2x
x²-2x-80=0
(x-10)(x+8)=0
∴x1=10 x2=-8
经检验：x1=10 x2=-8是原方程的解.