6x^4+5x^3-38x^2+5x+6
=(6x^4+5x^3-39x^2)+(x^2+5x+6)
=x^2(6x^2+5x-39)+(x+2)(x+3)
=x^2(x+3)(6x-13)+(x+2)(x+3)
=(x+3)(6x^3-13x^2+x+2)
=(x+3)(6x^3-13x^2+2x-x+2)
=(x+3)[x(6x^2-13x+2)-(x-2)]
=(x+3)[x(x-2)(6x-1)-(x-2)]
=(x+3)[(x-2)(6x^2-x-1)]
=(x+3)(x-2)(2x-1)(3x+1)