Question 482789
Take 1/2 of the coefficient of the {{{x}}} term,
then square it, then add it to both sides
{{{ x^2 + 15x + (15/2)^2 = 5 + (15/2)^2 }}}
{{{ x^2 + 15x + 225/4 = 20/4 + 225/4 }}}
{{{ ( x + 15/2 )^2 = 245/4 }}}
Take the square root of both sides
{{{ x + 15/2 = sqrt(245)/2 }}}
{{{ x = ( -15 +- sqrt(245)) / 2 }}}