Finding X coordinate corresponding to the user input Y coordinate from chart

Y - y1 = (X - x1)(y2 - y1)/(x2 - x1)

Y - 9 = (X  - 1)(10 - 9)/(2 - 1)

Y = X + 8



If X = 1.5 Then Y = 1.5 + 8 = 9.5

private double ComputeY(Point[] points, double x)
       {
          // points = (from p in points
          //          orderby p.X ascending
          //          select p).ToArray();

           var myPoints = (from p in points
                           where p.X >= x || p.X <= x
                           select p).Take(2);

           double x1, x2, y1, y2;
           if (myPoints.Count() == 2)
           {
               Point[] twoPoints = myPoints.ToArray();

               x1 = twoPoints[0].X;
               x2 = twoPoints[1].X;
               y1 = twoPoints[0].Y;
               y2 = twoPoints[1].Y;

               if (x2 - x1 == 0)
                   throw new Exception("Division by zero!");

               double z = (y2 - y1) / (x2 - x1);

               return x * z - x1 * z + y1;
           }

           throw new Exception("2 points not found");

           return 0;
       }

Point[] points = new Point[3] { new Point(1, 9), new Point(2, 10), new Point(3, 11) };


Console.WriteLine(ComputeY(points, 1.5));