You can easily find sample code of how to use IntersectWith() in VBA's documentation. With AutoCAD running:
1. Go to VBA editor (command "VBAIDE")
2. open Object Browser window
3. Select any object that has IntersectionWith method, such as AcadEntity, AcadLine, AcadCircle..., on the left side
4. Select IntersectionWith method on the right side
5. Click "?" on top of the Object Browser window. At this point, AutoCAD VBA help document window opens.
Here is the code copied from the VBA HELP document:
Sub Example_IntersectWith()
' This example creates a line and circle and finds the points at
' which they intersect.
' Create the line
Dim lineObj As AcadLine
Dim startPt(0 To 2) As Double
Dim endPt(0 To 2) As Double
startPt(0) = 1: startPt(1) = 1: startPt(2) = 0
endPt(0) = 5: endPt(1) = 5: endPt(2) = 0
Set lineObj = ThisDrawing.ModelSpace.AddLine(startPt, endPt)
' Create the circle
Dim circleObj As AcadCircle
Dim centerPt(0 To 2) As Double
Dim radius As Double
centerPt(0) = 3: centerPt(1) = 3: centerPt(2) = 0
radius = 1
Set circleObj = ThisDrawing.ModelSpace.AddCircle(centerPt, radius)
ZoomAll
' Find the intersection points between the line and the circle
Dim intPoints As Variant
intPoints = lineObj.IntersectWith(circleObj, acExtendNone)
' Print all the intersection points
Dim I As Integer, j As Integer, k As Integer
Dim str As String
If VarType(intPoints) <> vbEmpty Then
For I = LBound(intPoints) To UBound(intPoints)
str = "Intersection Point[" & k & "] is: " & intPoints(j) & "," & intPoints(j + 1) & "," & intPoints(j + 2)
MsgBox str, , "IntersectWith Example"
str = ""
I = I + 2
j = j + 3
k = k + 1
Next
End If
End Sub
HTH