Hi sdecorme,
It's quite easy to do a threepoint linear regression. Here is some code:
BivariateSample sample = new BivariateSample();
sample.Add(0, 0);
sample.Add(100, 100);
sample.Add(x, y);
LinearRegressionFitResult result = sample.LinearRegression();
When it returns, result will contain data about the bestfit line and goodness of fit.
If you are looking for analytic formulas for a and b as functions of x and y, you won't get that from a numerical library. But it's not hard to derive such a formula using the formulas for a and b as functions of input points that you can find in any textbook
that covers linear regression.
