# Geometric inverse of infinity

1. Oct 22, 2014

### Pjpic

I seem to recall reading a geometry method that showed zero to be the inverse of infinity. Can you give me a reference for that?

2. Oct 22, 2014

### HallsofIvy

That depends upon what you mean. "Inverse" in what sense? You can, for example, use "inversion" in a circle. Given a circle of radius "R" and center "O" and a point P inside the circle, we define its "inverse" to be the point, Q, lying on the same extended radius of the circle as P, such that |OP||OQ|= R^2 where |OP| and |OQ| are the distances from O to the two points. If P is on the circle, Q= P. As we move P closer to the center of the circle, the corresponding Q moves farther and farther from the circle. As P approaches the center, in the limit, Q goes to infinity.

But if you are looking for a "proof", geometrical or otherwise, that, in our usual arithmetic 1/0 is equal to infinity, that just isn't going to happen. It simply isn't true. There is no number called "infinity" in our usual arithmetic and you cannot divide 1, or any other number, by 0. "Infinity" is just a "shorthand" for limits.

3. Oct 22, 2014

### ellipsis

Asking what 1/0 is is like asking what the color of an electron is. Or, whether or not the king of France is bald!

4. Oct 23, 2014

### HallsofIvy

NO! I am not bald!