sextant - 2006-07-13

I have been trying to find an equation that will rotate a quadratic equation about it’s vertex.

The value (of rotation) is at this point unknown and arbitrary given that I am trying to discover a parabolic curve with very specific properties.

So far I have been trying to manipulate y=a-(x-h)^2 +k empirically in order to answer a critical design question. 

Is anyone able to answer this question; How to trigonometrically rotate y=a-(x-h)^2 +k about it’s vertex? (or in fact is it possible?)