Đáp án:
a, x²-2xy+x-2y=x(x-2y)+x-2y=(x-2y)(x+1)
b, 12x-9-4x²=-(4x²-12x+9)=-(2x-3)²
c,(x²-4x+6)/(x-2)=[(x-2)²+2]/(x-2)=x-2+2/(x-2)
d, (4x-5)(2x+3)-4(x+2)(2x-1)+(10x+7)=8x²-10x+12x-15-8x²-16x+4x+8+10x+7=30
e, x(x-y)-y(x+y)+x²+y²=x²-xy-xy-y²+x²+y²=2x²-2xy=2x(x-y)
f, (1/2x-y)²=x²/4-xy+y²