（-ab+2)(5ab-3)-ab(1-ab)
=-5a^2b^2+13ab-6-ab+a^2b^2
=-4a^2b^2+12ab-6
(-2x)·(x^2-5x+6)-4x(2x^2-3x+1)
=-2x^3+10x^2-12x-8x^3+12x^2-4x
=-10x^3+22x^2-16x