Finding Bitmap's Head Formula?

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VB

.NET

DirectX

mathematics

I'm trying to find Bitmap's head... umm it's too hard to describe for my bad english... :(

+-o-+
|   |
|   |
|   |
+---+

This is what i want
(o mark is Bitmap's head)

It's easy when Bitmap is not rotated.
If Bitmap rotated 90' degree will change like this:

+------+
|      o
+------+

I made this formula but it's not perfect what i expected.
(it's only work Bitmap's Height is bigger than Width)

Formula:

X = 1 + (Math.Sin(DegreeToRadian(Angle)) * 2) * (Me.Height / 4)
Y = 2 + (-Math.Cos(DegreeToRadian(Angle)) * 2) * (Me.Height / 4)

I'm so sorry for my bad describe and english ..:O