Question 1186777


 {{{f(x)=x^2 +8x}}}

Solve {{{f(x)=-16}}}

{{{-16=x^2 +8x}}}

{{{0=x^2 +8x+16}}}.........write as a square of the sum 

{{{0=x^2 +8x+4^2}}}

{{{0=(x+4)^2}}}

solution:

{{{0=(x+4)}}}=>{{{x=-4}}}