Помогите устранить ошибку в тексте программы

Dim a1 As Double, a2 As Double, a3 As Double
Dim b1 As Double, b2 As Double
Dim A As Double, B As Double, e As Double
Dim N As Double, K As Double
Dim x As Double, x1 As Double, x2 As Double, y1 As Double, y2 As Double
Private Sub CommandButton3_Click()
    a1 = CDbl(TextBox1.Value)
    a2 = CDbl(TextBox2.Value)
    a3 = CDbl(TextBox3.Value)
    b1 = CDbl(TextBox4.Value)
    b2 = CDbl(TextBox5.Value)
    A = TextBox7.Value
    B = TextBox6.Value
    e = TextBox8.Value
    N = F(A)
    K = F(B)
    If N * K > 0 Then
        MsgBox ("Введите новые значения отрезка")
    Else
        x1 = Newton1(A)
        x2 = Newton2(B)
        F1 = F(x1)
        F2 = F(x2)
        Do While Abs(B - A) > e
            If F1 > F2 Then
                B = x2
                x2 = x1
                F2 = F1
                x1 = Newton1(A)
                F1 = F(x1)
            Else
                A = x1
                x1 = x2
                F1 = F2
                x2 = Newton2(B)
                F2 = F(x2)
            End If
        Loop
        x = (A + B) / 2
        Label13.Caption = Round(x, 2)
        Label14.Caption = Round(F(x), 2)
    End If
End Sub
 
Function F(x)
    F = (a1 * x ^ 2 + a2 * x + a3) - (b1 * x + b2)
End Function
 
Function Proizvodnaya(x)
    Proizvodnaya = 2 * a1 * x + a2 - b1
End Function
 
Function Newton1(A)
    Newton1 = A - (F(A) / Proizvodnaya(A))
End Function
 
Function Newton2(B)
    Newton2 = B - (F(B) / Proizvodnaya(B))
End Function
 
Private Sub CommandButton5_Click()
Range("E2:F4").Select
Selection.ClearContents
Range("G5").Select
    Unload UserForm1
End Sub
 
Private Sub CommandButton4_Click()
        TextBox1.Value = ""
        TextBox2.Value = ""
        TextBox3.Value = ""
        TextBox4.Value = ""
        TextBox5.Value = ""
        TextBox6.Value = ""
        TextBox7.Value = ""
        TextBox8.Value = ""
        Label13.Caption = ""
        Label14.Caption = ""
Range("E2:F4").Select
        Selection.ClearContents
        Range("G5").Select
    
End Sub
Private Sub CommandButton1_Click()
Dim x As Double, y As Double, i As Integer
     i = 2
Do While Cells(i, 1) <> Empty
x = Cells(i, 1)
y = Cells(i, 3)
x_1st = x_1st + x
x_2st = x_2st + x ^ 2
x_3st = x_3st + x ^ 3
x_4st = x_4st + x ^ 4
x_2st_y = x_2st_y + (x ^ 2 * y)
x_y = x_y + (x * y)
y_1st = y_1st + y
i = i + 1
Loop
a_1 = ((x_2st_y * x_2st * (i - 2)) + (x_3st * x_1st * y_1st) _
+ (x_y * x_1st * x_2st) - (x_2st ^ 2 * y_1st) - (x_y * x_3st * (i - 2)) _
- (x_1st ^ 2 * x_2st_y)) / ((x_4st * x_2st * (i - 2)) _
+ 2 * (x_1st * x_2st * x_3st) - (x_2st ^ 3) - (x_3st ^ 2 * (i - 2)) _
- (x_1st ^ 2 * x_4st))
a1 = Round(a_1, 3)
Cells(2, 5) = a1
TextBox1.Value = CStr(a1)
a_2 = ((x_4st * x_y * (i - 2)) + (x_2st_y * x_1st * x_2st) _
+ (x_3st * y_1st * x_2st) - (x_2st ^ 2 * x_y) - (x_3st * x_2st_y * (i - 2)) _
- (y_1st * x_1st * x_4st)) / ((x_4st * x_2st * (i - 2)) _
+ 2 * (x_3st * x_1st * x_2st) - (x_2st ^ 3) - (x_3st ^ 2 * (i - 2)) _
- (x_1st ^ 2 * x_4st))
a2 = Round(a_2, 3)
Cells(3, 5) = a2
TextBox2.Value = CStr(a2)
a_3 = ((x_4st * x_2st * y_1st) + (x_3st * x_y * x_2st) _
+ (x_3st * x_1st * x_2st_y) - (x_2st ^ 2 * x_2st_y) - (x_3st ^ 2 * y_1st) _
- (x_1st * x_y * x_4st)) / ((x_4st * x_2st * (i - 2)) _
+ 2 * (x_3st * x_1st * x_2st) - (x_2st ^ 3) - (x_3st ^ 2 * (i - 2)) _
- (x_1st ^ 2 * x_4st))
a3 = Round(a_3, 3)
Cells(4, 5) = a3
TextBox3.Value = CStr(a3)
End Sub
Private Sub CommandButton2_Click()
Dim x As Double, y As Double, i As Integer
i = 2
Do While Cells(i, 1) <> Empty
x = Cells(i, 1)
y = Cells(i, 2)
x_1st = x_1st + x
x_2st = x_2st + x ^ 2
x_3st = x_3st + x ^ 3
x_4st = x_4st + x ^ 4
x_2st_y = x_2st_y + (x ^ 2 * y)
x_y = x_y + (x * y)
y_1st = y_1st + y
i = i + 1
Loop
b_1 = ((x_4st * x_y * (i - 2)) + (x_2st_y * x_1st * x_2st) _
+ (x_3st * y_1st * x_2st) - (x_2st ^ 2 * x_y) - (x_3st * x_2st_y * (i - 2)) _
- (y_1st * x_1st * x_4st)) / ((x_4st * x_2st * (i - 2)) _
+ 2 * (x_3st * x_1st * x_2st) - (x_2st ^ 3) - (x_3st ^ 2 * (i - 2)) _
- (x_1st ^ 2 * x_4st))
b1 = Round(b_1, 3)
Cells(2, 6) = b1
TextBox4.Value = CStr(b1)
b_2 = ((x_4st * x_2st * y_1st) + (x_3st * x_y * x_2st) _
+ (x_3st * x_1st * x_2st_y) - (x_2st ^ 2 * x_2st_y) - (x_3st ^ 2 * y_1st) _
- (x_1st * x_y * x_4st)) / ((x_4st * x_2st * (i - 2)) _
+ 2 * (x_3st * x_1st * x_2st) - (x_2st ^ 3) - (x_3st ^ 2 * (i - 2)) _
- (x_1st ^ 2 * x_4st))
b2 = Round(b_2, 3)
Cells(3, 6) = b2
TextBox5.Value = CStr(b2)
End Sub
 
Private Sub UserForm_Initialize()
Label13.Caption = ""
Label14.Caption = ""
End Sub