Thanks for all the help to my beginner's questions. This time, I have a question regarding practical use of geometry. Say I have a cylinder of radius r. And I "cut it" (a cross-section) in the middle. If I cut it perpendicular to the axis, simple enough I will have a circle of radius r.
Now, what happens when I cut it non-perpendicularly at an angle $\alpha$ with respect to the axis?
I get an ellipse! Fair enough! And an ellipse has two focal points (foci?), F1 and F2. All right, but what I would like to know is how to calculate data about these foci. i.e, the distance between those and the distance between any point in the ellipse to these foci
Any advice greatly appreciated