Question

(x+3)(x-4)(x+5)(x-6)+80

Answer 1

原式=[(x²-x)-12][(x²-x)-30]+80

=(x²-x)²-42(x²-x)+360+80

=(x²-x)²-42(x²-x)+440

=(x²-x-20)(x²-x-22)

=(x-5)(x+4)(x²-x-22)