Question

因式分解xxxx+8xxx+15xx-4x-20

Answer 1

x^4+8x^3+15x^2-4x-20

=x^2(x^2+8x+15)-4(x+5)

=x^2(x+5)(x+3)-4(x+5)

=(x+5)[(x+3)x^2-4]

=(x+5)(x^3+3x^2-4)

=(x+5)(x^3+2x^2+x^2-4)

=(x+5)[x^2(x+2)+(x+2)(x-2)]

=(x+5)(x+2)(x^2+x-2)

=(x+5)(x+2)(x-1)(x+2)

=(x+5)(x-1)[(x+2)^2]