2x四次方+x三次方-20x平方-13x+30有因式2x+5和x-3
设2x四次方+x三次方-20x平方-13x+30=(2x+5)(x-3)(x^2+ax+b)
2x四次方+x三次方-20x平方-13x+30=(2x^2-x-15)(x^2+ax+b)
2x四次方+x三次方-20x平方-13x+30=2x^4+(2a-1)x^3+(2b-a-15)x^2-(b+15a)x-15b
(2a-1)=1 (2b-a-15)=-20 -(b+15a)=-13 -15b=30
a=1 b=-2
2x四次方+x三次方-20x平方-13x+30
=(2x+5)(x-3)(x^2+x-2)
=(2x+5)(x-3)(x-1)(x+2)