Question 196370
 {{{x^2+8x= -16}}}
Using the complete the square method:
 {{{x^2 + 8x + (8/2)^2 = -16 + (8/2)^2}}}
The left side is a perfect square
{{{(x + 4)^2 = -16 + 16}}}
{{{(x + 4)^2 = 0}}}
{{{x + 4 = 0}}}
{{{x = -4}}}
This is a double root at {{{x = -4}}}
I'll plot the function
 {{{ graph( 300, 300, -10, 1, -1, 10,  x^2 + 8x + 16) }}}