Answer :

[tex]2x^2+2x-7x-7=2x(x+1)-7(x+1)=(2x-7)(x+1)=\\ \\=2(x-3.5)(x+1)\\ \\2x^2-5x-7=0\ \ \ \Leftrightarrow\ \ \ 2(x-3.5)(x+1)=0\\ \\x-3.5=0\ \ \vee\ \ \ x+1=0\\ \\.\ \ \ \ \ \ \ x=3.5\ \ \ \ \ \ \ \ \ \ \ x=-1[/tex]