因式分解
问题描述：
因式分解
1.-1+y+20y^2
2.(x^2-3x-5)(x^2-3x+2)+6
3.(x+1)(x+3)(x+5)(x+7)+15
答
1.-1+y+20y^2=(4y+1)(5y-1)2.(x^2-3x-5)(x^2-3x+2)+6=(x^2-3x-5)^2+7(x^2-3x-5)+6=(x^2-3x-5+1)(x^2-3x-5+6)=(x^2-3x-4)(x^2-3x+1)=(x^2-3x+1)(x+1)(x-4)3.(x+1)(x+3)(x+5)(x+7)+15 = (x^2+8x+7)(x^2+8x+15)+15 =(x^...