so we first minus 6 both sides
7x^2-14x=-6
then we have
A(x^2-2x)=-6
what is A?
hmm (this should be painfully obvous, but if not, here are steps)
7x^2-14x=-6
A(x^2-2x)=-6
7x^2-14x=-6=A(x^2-2x)
7x^2-14x=A(x^2-2x)
undistribute 7
7(x^2-2x)=A(x^2-2x)
divide both sides by (x^2-2x)
7=A
A=7
