Assuming I have a semi-circle with a diameter of 100, is there a formula where I can plug in X and get the Y of the semi-circle?

For example, assuming a 'U' shaped semi-circle, where X:0 is the top-left of the semi-circle, X:100 is the top-right, and Y:0 is the bottom-center, what formula would I use to get Y at any X position?

If possible, I would appreciate if the formula was an exact representation of a circle, not an approximation.

Thanks in advance for your help