程序代码：

Private Sub Command1_Click()
Text4.Text = ""
Text5.Text = ""
Dim A As Single, B As Single, C As Single
Dim D As Single, X1 As Single, X2 As Single
Dim R As Single, P As Single
  A = Val(Text1.Text)
  B = Val(Text2.Text)
  C = Val(Text3.Text)
  If A = 0 Then
     MsgBox "一元二次方程的系数A不能为0"
     Exit Sub
  Else
     D = B ^ 2 - 4 * A * C
     R = -B / (2 * A)
     If D = 0 Then
        Text4.Text = "相等实数根：" & vbCrLf
        Text4.Text = Text4.Text & R
        Text5.Text = "相等实数根：" & vbCrLf
        Text5.Text = Text5.Text & R
     ElseIf D > 0 Then
        X1 = (-B + Sqr(D)) / (2 * A)
        X2 = (-B - Sqr(D)) / (2 * A)
        Text4.Text = "不相等实数根：" & vbCrLf
        Text4.Text = Text4.Text & X1
        Text5.Text = "不相等实数根：" & vbCrLf
        Text5.Text = Text5.Text & X2
     ElseIf D < 0 Then
        P = Sqr(-D) / 2 * A
        Text4.Text = "不相等虚数根：" & vbCrLf
        Text4.Text = Text4.Text & R & "+" & P & "i"   '其中 i 是虚数单位，就是-1的平方根，只有在D小于0时才有虚数根。
        Text5.Text = "不相等虚数根：" & vbCrLf
        Text5.Text = Text5.Text & R & "-" & P & "i"
     End If
  End If
End Sub