Программа не правильно вычисляет углы

Option Strict On
Option Explicit On
Imports System.Math
Public Class form1
    
    Function vvod(ByVal T As TextBox) As Single
        Return CSng(Val(T.Text))
    End Function
 
    Sub vivod(ByVal Z As Single, ByVal T As TextBox)
        T.Text = CStr(Z)
    End Sub
    Public Function cosinus(ByVal x1 As Double, _
                  ByVal y1 As Double, ByVal x2 As Double, _
                  ByVal y2 As Double) As Double
        Return CSng(x1 * x2 + y1 * y2) / ((x1 ^ 2 + y1 ^ 2) ^ 0.5 * (x2 ^ 2 + y2 ^ 2) ^ 0.5)
    End Function
 
 
    Sub ab(ByVal x1 As Double, ByVal y1 As Double, _
           ByVal x2 As Double, ByVal y2 As Double, _
           ByVal x3 As Double, ByVal y3 As Double, _
           ByRef a As Double, ByRef b As Double)
        Dim cos1, cos2 As Double
        cos1 = cosinus(x1, y1, x2, y2)
        cos2 = cosinus(x2, y2, x3, y3)
 
        a = CSng(Atan(-cos1 / (-cos1 * cos1 + 1) ^ (1 / 2) + 2 * Atan(1)))
        b = CSng(Atan(-cos2 / (-cos2 * cos2 + 1) ^ (1 / 2) + 2 * Atan(1)))
 
    End Sub
    Private Sub Button1_Click(ByVal sender As System.Object, _
            ByVal e As System.EventArgs) Handles Button1.Click
        Dim x1 As Double, x2 As Double, x3 As Double
        Dim y1 As Double, y2 As Double, y3 As Double
        Dim угол2 As Double, угол1 As Double
        x1 = vvod(TextBox1) : x2 = vvod(TextBox3) : x3 = vvod(TextBox5)
        y1 = vvod(TextBox2) : y2 = vvod(TextBox4) : y3 = vvod(TextBox6)
        ab(x1, y1, x2, y2, x3, y3, угол1, угол2)
        vivod(CSng(угол1), TextBox7) : vivod(CSng(угол2), TextBox8)
 
    End Sub
    Private Sub Button2_Click(ByVal sender As System.Object, _
               ByVal e As System.EventArgs) Handles Button2.Click
        End
    End Sub
 
End Class