since (8/2)^2=16, we will add 16 in both sides of the equation, obtaining
[tex]x^2+8x+16=1[/tex]now, we factor the left side of the equation (it's a perfect square)
[tex](x+4)^2=1[/tex]then we have two options or x+4=1 or x+4=-1
solving both of the we have that the values for x are x=-3 and x=-5