Find the vertex of the parabola. Sketch the graph: y=-x^2+2x-3
or maybe (b,-c), but that is the idea.
You never will find the vertex of the parabola unless you make some effort. I seriously doubt this problem dropped out of the sky and hit you on the head. I am almost certain there was a lecture or a section in book right before you encountered this problem. There was that Algebra I class, however long ago, where you discussed "Completing the Square". All these things can work for your good.