Integral Calculus

For everyone who hasn't any desire to to type every integral calculus into the calculator, I have a solution:

Public Class Form1
Dim a As Double
Dim b As Double
Dim n As Double
Dim F As Double

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

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
If TextBox1.Text = "" Or TextBox2.Text = "" Or TextBox4.Text = "" Then
MessageBox.Show("Bitte Eingabe überprüfen", "Error", MessageBoxButtons.OK)
Else
a = TextBox2.Text
b = TextBox4.Text
n = TextBox1.Text

F = ((b ^ (n + 1)) / (n + 1)) - ((a ^ (n + 1)) / (n + 1))

TextBox3.Text = F
End If
End Sub

Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
TextBox1.Text = ""
TextBox2.Text = ""
TextBox3.Text = ""
TextBox4.Text = ""
End Sub
End Class

Here you can download my program:
http://christianlachmann.de.vu/Integralrechnung.exe