You don't. That is a whole set of quadratic equations. The set has infinite elements; one for each possible real value of . Without another relationship defined, you cannot determine which element of the set you are dealing with.
You can apply the quadratic formula to get an expression for the solution:
, , and
You will probably want to specify an interval for such that the roots of the equation will have real values.
My calculator said it, I believe it, that settles it