Drawing an arc with three points ..?

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C#

C#4.0

Drawing an arc with three points ..??
Help me to find this..



private void Form1_MouseDown(object sender, MouseEventArgs e)
{
Graphics gs = this.CreateGraphics();

if (pt[0].X == 0 && pt[0].Y == 0)
{

pt[0].X = e.X;
pt[0].Y = e.Y;
}
else if (pt[1].X == 0 && pt[1].Y == 0)
{

pt[1].X = e.X;
pt[1].Y = e.Y;
}
else if (pt[2].X == 0 && pt[2].Y == 0)
{

pt[2].X = e.X;
pt[2].Y = e.Y;

double dstart = Math.Atan2(pt[0].Y - pt[1].Y, pt[0].X - pt[1].X) * Rad2Deg;



double dEnd = Math.Atan2(pt[0].Y - pt[2].Y, pt[0].X - pt[2].X) * Rad2Deg;

double dSweep = dEnd - dstart;

PointF pMid = new PointF((pt[0].X + pt[2].X) / 2, (pt[0].Y + pt[2].Y) / 2);

double a = pMid.X - pt[0].X;
double b = pMid.Y - pt[0].Y;
double radius = Math.Sqrt(a * a + b * b);

double a1 = pMid.X - pt[1].X;
double b1 = pMid.Y - pt[1].Y;
double radius1 = Math.Sqrt(a1 * a1 + b1 * b1);



gs.DrawArc(Pens.Black, pt[0].X, pt[0].Y, Convert.ToInt32(radius * 2), Convert.ToInt32(radius1), Convert.ToInt32(dstart), Convert.ToInt32(dSweep));


}
}