I’ve been busy building an enzymatic assay to measure a protein. The data points of the standards used to create a calibration curve, when graphed, fit perfectly on a second order polynomial curve (i.e. aX^2+bX+c). I remember the formula for solving for X when Y=0, however, we’re in the real world, and I need to find X when, say, 1.225=aX^2+bX+c. From Excel, I know a, b, and c, and from my experimental data, I know Y. What I need to know, and can’t find, is how to solve for X when Y has an explicit value not equal to 0. Any help from those more mathematically inclined than I would be greatly appreciated.