Public Function Quadratische_Gleichung _
        (ByVal p As Double, ByVal q As Double, _
        ByRef L1 As Double, ByRef L2 As Double) As Boolean
 
     'für Prüfung gegen 0
     Const epsilon As Double = 0.000000001
 
     'Diskriminante berechnen
     Dim disk As Double
     diskr = (p / 2#) * (p / 2#) - q
 
     'Fallunterscheidung
     If Abs(diskr) < epsilon Then
        'Diskriminante wird als 0 eingeordnet
        L1 = -p / 2: L2 = 0#
        Quadratische_Gleichung = True
    ElseIf diskr >= epsilon Then
        'positive Diskriminante
        L1 = -p / 2# - Sqr(diskr)
        L2 = -p / 2# + Sqr(diskr)
        Quadratische_Gleichung = True
    Else
        'negative Diskriminante (nicht lösbar)
        L1 = 0: L2 = 0
        Quadratische_Gleichung = False
    End If
End Function

Sub QuadratischeGleichung()
' QuadratischeGleichung Makro
 
  Dim row As Integer
  Dim p As Double, q As Double, L1 As Double, L2 As Double
  For row = 1 To 100
      Tabelle1.Cells(row, 3) = "": Tabelle1.Cells(row, 4) = ""
      If IsNumeric(Tabelle1.Cells(row, 1)) And _
            IsNumeric(Tabelle1.Cells(row, 2)) Then
            p = Tabelle1.Cells(row, 1): q = Tabelle1.Cells(row, 2)
            If p <> 0 And q <> 0 Then
                If Quadratische_Gleichung(p, q, L1, L2) Then
                    Tabelle1.Cells(row, 3) = L1
                    If L2 <> 0# Then Tabelle1.Cells(row, 4) = L2
                Else
                    Tabelle1.Cells(row, 3) = "nicht lösbar"
                    Tabelle1.Cells(row, 4) = "nicht lösbar"
                End If
            End If
        End If
   Next row
End Sub