Bezier Curve equation

Hello,

My model involves drawing a second order Bezier curve, and as part of it I have to be able to get the "Y" value on the curve for a certain "X" value. Normally that wouldn't be an issue because it's a matter of playing with quadratics, however the points calculated are close... but wrong. What equation does Comsol use (factoring in the weights) to generate to Bezier curve, or if that information isn't available, how can I go about mapping an "X" coordinate onto the curve.

Thanks,
Aaron Shifman