Ошибка в определении области Range

Sub Кнопка2_Щелкнуть()
Dim objChart As ChartObject
Dim myRange As Range
' Расчитываем исходные данные графика
Pi = 3.1415
a = CDbl(Cells(4, 1))
b = CDbl(Cells(4, 2))
i = 9
For x = a To b Step (b - a) / 20
If x < (-1) * Pi Then y = Tan(x) ^ 2
If (x >= (-1) * Pi) And (x <= 0) Then y = x - 2 * Sin(0.5 * x)
If x > 0 Then y = 2.25
Cells(i, 1) = x
Cells(i, 2) = y
i = i + 1
Next x
' создаем график с необходимыми параметрами
    Charts.Add
    ActiveChart.ChartType = xlXYScatterSmooth
    ActiveChart.SetSourceData Source:=Sheets("Задание 4").Range("A8:B29"), PlotBy:= _
        xlColumns
    ActiveChart.Location Where:=xlLocationAsObject, Name:="Задание 4"
    With ActiveChart
        .HasTitle = False
        .Axes(xlCategory, xlPrimary).HasTitle = True
        .Axes(xlCategory, xlPrimary).AxisTitle.Characters.Text = "x"
        .Axes(xlValue, xlPrimary).HasTitle = True
        .Axes(xlValue, xlPrimary).AxisTitle.Characters.Text = "y"
    End With
    With ActiveChart
        .HasAxis(xlCategory, xlPrimary) = True
        .HasAxis(xlValue, xlPrimary) = True
    End With
    ActiveChart.Axes(xlCategory, xlPrimary).CategoryType = xlAutomatic
    With ActiveChart.Axes(xlCategory)
        .HasMajorGridlines = True
        .HasMinorGridlines = False
    End With
    With ActiveChart.Axes(xlValue)
        .HasMajorGridlines = True
        .HasMinorGridlines = False
    End With
   ActiveChart.HasLegend = False
      With Selection.Border
        .ColorIndex = 16
        .Weight = xlThin
        .LineStyle = xlDot
    End With
    With Selection.Interior
        .ColorIndex = 2
        .PatternColorIndex = 1
        .Pattern = xlSolid
    End With
    ActiveChart.Axes(xlValue).MajorGridlines.Select
    With Selection.Border
        .ColorIndex = 57
        .Weight = xlHairline
        .LineStyle = xlDash
    End With
    ActiveChart.Axes(xlCategory).MajorGridlines.Select
    With Selection.Border
        .ColorIndex = 57
        .Weight = xlHairline
        .LineStyle = xlDash
    End With
       ActiveChart.Axes(xlValue).AxisTitle.Select
    With Selection
        .HorizontalAlignment = xlCenter
        .VerticalAlignment = xlCenter
        .ReadingOrder = xlContext
        .Orientation = xlHorizontal
    End With
    ' располагаем график в месте расположенном для этого
    Set myRange = Worksheets(4).Range("С9:С20")
    With objChart
        .Left = myRange.Left
        .Top = myRange.Top
        .Width = myRange.Width
        .Height = myRange.Height
    End With
Set myRange = Nothing
End Sub

 Set myRange = Worksheets(4).Range("С9:С20")