Метод хорд, Ньютона и половиного деления - VB

Dim a, b, c, c1 As Single
Dim n As Integer
Private Function F(ByVal x As Double) As Double
    F = x - 3 - Sin(3 * x)
End Function
Private Function F1(ByVal x As Double) As Double
    F1 = 9 * Sin(3 * x)
End Function
 
Private Sub Command1_Click()
'metod polovinogo deleniya
a = Val(Text1.Text)
b = Val(Text2.Text)
e = 0.000001
    Do While Abs(b - a) > e
        c = F(a)
        c1 = F((a + b) / 2)
        If (c > 0 And c1 > 0) Or (c < 0 And c1 < 0) Then
            a = a / 2 + b / 2
        Else
            b = a / 2 + b / 2
        End If
    Loop
Text3.Text = Round(a / 2 + b / 2, 5)
End Sub
 
Private Sub Command2_Click()
'metod newton
    a = Val(Text1.Text)
    b = Val(Text2.Text)
    n = 1
    Do While F(c) * F(c1) > 0
        c = a + 3 * (b - a) / n
        c1 = a + (3 + 1) * (b - a) / n
        n = n + 1
    Loop
    If F(c) * F1(c) < 0 Then Text3.Text = Round(c1, 5) Else Text3.Text = Round(c, 5)
End Sub
 
Private Sub Command3_Click()
'metod hord
    a = Val(Text1.Text)
    b = Val(Text2.Text)
    e = 0.000001
    Do While Abs(b - a) > e
        c = b - F(b) * (b - a) / (F(b) - F(a))
        a = b
        b = c
    Loop
Text3.Text = Round(b, 5)
End Sub