Question 1090213
Take half of the x coefficient, square it, add to both sides.
{{{n^2-16n=72}}}
{{{n^2-16n+(16/2)^2=72+(16/2)^2}}}
{{{n^2-16n+64=138}}}
{{{(n-8)^2=138}}}
{{{n-8=0 +- sqrt(138)}}}
{{{highlight(n=8 +- sqrt(138))}}}