[tex]\begin{cases} x=-7\implies &x+7=0\\ x=0\implies &x=0\\ x=1\implies &x-1=0\\ x=6\implies &x-6=0 \end{cases}\qquad \implies (x+7)(x)(x-1)(x-6)=\stackrel{y}{0} \\\\\\ (x+7)(x)\stackrel{using~\mathbb{FOIL}}{(x^2-7x+6)}=0\implies (x^2+7x)(x^2-7x+6)=0[/tex]
[tex]\begin{array}{llll} x^2-7x+6\\ \qquad \times ~x^2\\\cline{1-1} x^4-7x^3+6x^2 \end{array}\qquad +\qquad \begin{array}{llll} x^2-7x+6\\ \qquad \times ~7x\\\cline{1-1} 7x^3-49x^2+42x \end{array} \\\\\\ (x^4-7x^3+6x^2)+(7x^3-49x^2+42x)=0 \\\\[-0.35em] ~\dotfill\\\\ ~\hfill x^4-43x^2+42x=y~\hfill[/tex]
