This is the basis of touch screen math calculations I'm working on. Just so happens, I tend to forget simple calculations. Especially where I don't even know the theta in the picture above is called? (The smaller angle of line and X-axis where the line intersects two arbitrarily given Vector2D points on a 2D plane? The atan2 angle?)
Anyway, I'm looking for the answer to the question: Is the theta the answer to atan2(Vector 1, Vector 2)?