Question 997140
You do NOT get rid of the exponent.  


Simplify and try to factorize.


{{{x^2-12x=90}}}
{{{x^2-12x-90=0}}}, factors in prime form for the constant,  3*3*2*5, and you might find in there, 6*15, something to test-try.


?
(x___6)(x____15)------no ; not work.
?
5*18 neither will work.


Discriminant?
{{{(-12)^2-4*1*(-90)}}}
{{{144+360}}}
{{{504}}}, not a perfect square, but a positive value.


Factorization will basically "not" work.
Formula for general solution to a quadratic equation gives 
{{{x=(12+- sqrt(504))/2}}}


{{{x=(12+- 2*sqrt(126))/2}}}


{{{highlight(x=6+- sqrt(126))}}}
or
{{{highlight(highlight(x=6+- 3*sqrt(2*7)))}}}