Using formula method to solve equation (2x + 8) (X-2) = x & sup2; + 2x-17

Using formula method to solve equation (2x + 8) (X-2) = x & sup2; + 2x-17

2x²-4x+8x-16=x²+2x-17
x²+2x+1=0
△=4-4=0
x=-2/2=-1