This is a linear equation rather than quadratic. You have x^2 on both sides and it will cancel.
If you take x^2-3x from both sides you will get which simplifies to
It follows that is the solution because whereas gives
edit: as a background you can have one solution to a quadratic equation (technically 2 equal roots). This happens when the discriminant is equal to 0.
For example find the solution(s) to (answer in spoiler)