[tex] (6x^4-5x^3-6x)-(7x-6x^3+2x^4)\\\\=6x^4-5x^3-6x-(+7x)-(-6x^3)-(+2x^4)\\\\=6x^4-5x^3-6x-7x+6x^3-2x^4\\\\=(6x^4-2x^4)+(-5x^3+6x^3)+(-6x-7x)\\\\=4x^4+x^3-13x [/tex]
