1)a=21 a=-21x²+21x+20=(x+1)(x+20)x²-21x+20=(x-1)(x-20)2)a=12 a=-12x²+12x+20=(x+2)(x+10)x²-12x+20=(x-2)(x-10)3)a=9 a=-9x²+9x+20=(x+4)(x+5)x²-9x+20=(x-4)(x-5)