Fitting line while minimizing least squares error

simpleLineFitting.cs

Tuple<double, double> LinearLeastSquaresFit(List<Point> points)
{
    double length = points.Count;
    double Sx = points.Sum(p=> p.X);
    double Sy = points.Sum(p => p.Y);
    double Sxx = points.Sum(p => Math.Pow(p.X,2));
    double Sxy = points.Sum(p => p.X * p.Y); 

    var a = (Sxy * length - Sx * Sy) / (Sxx * length - Sx * Sx);
    var b = (Sxy * Sx - Sy * Sxx) / (Sx * Sx - length * Sxx);

    return new Tuple<double, double>(a, b);
}