Solving quadratic formulas

I wrote an application with VisualBasic 2008 to solve quadratic formulas.

The most important part is this:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click



a = TextBox1.Text
b = TextBox2.Text
c = TextBox3.Text

x3 = ((b ^ 2) - (4 * a * c))

If x3 < 0 Then
TextBox4.Text = "D < 0"
TextBox5.Text = "D < 0"
MessageBox.Show("D<0", "Fehler", MessageBoxButtons.OK)
Else

x1 = (-b - Math.Sqrt((b ^ 2) - (4 * a * c))) / (2 * a)
x2 = (-b + Math.Sqrt((b ^ 2) - (4 * a * c))) / (2 * a)

TextBox4.Text = x1
TextBox5.Text = x2
End If
End Sub

Here, x1 and x2 is calculated and checked whether the discriminant is smaller than zero.  In VB you use Math.Sqrt ( ) to extract a root.

You can download this application here:
http://christianlachmann.de.vu/QuadratischeGleichung.exe

But it's in German language.