x2-5x+6=(x-2)(x-3)
x2-21x-100=(x-25)(x+4)
x2-15x-100=x2-20x+5x-20x5=(x-20)(x+5)
x2-100=x2-10x+10x-10x10=(x-10)(x+10)
x2+13x-90=x2-5x+18x-5x18=(x-5)(x+18)
x2-16x-80=x2-20x+4x-20x4=(x-20)(x+4)
x2-9x-80=x2-16x+5x-16x5=(x-16)(x+5)
x2+42x+80=x2+2x+40x+2x40=(x+2)(x+40)
x2+38x-80=x2-2x+40x-2x40=(x-2)(x+40)
x2-7x-18=x2-9x+2x-9x2=(x-9)(x+2)