解
(x-2)²-2(x+1)(x-1)-x(2x-1)
=x²-4x+4-2(x²-1)-2x²+x
=x²-4x+4-2x²+2-2x²+x
=(x²-2x²-2x²)+(-4x+x)+6
=-3x²-3x+6