Question 1087553
There's an error in your formula,
{{{x^2+2x-8=0}}}
{{{a=1}}}
{{{b=2}}}
{{{c=-8}}}
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} 
{{{x = (-2 +- sqrt( (-2)^2-4*1*(-8) ))/(2*1) }}} 
{{{x = (-2 +- sqrt( 4+32 ))/2 }}} 
{{{x = (-2 +- sqrt( 36 ))/2 }}} 
Take it from there and finish.