Complexinfinity

[Andrew26]

What is infinity+i, infinity i+1 and infinity i+infinity?

i being the square root of -1 - the imaginary unit.

[uncool]

Infinity is usually not thought of as a number; though there are some cases where you can think of it as a number, those cases treat infinity in different ways, meaning that to answer your question, I'd have to ask what you are trying to do with these "numbers".

[studiot]

4 hours ago, uncool said:

 meaning that to answer your question, I'd have to ask what you are trying to do with these "numbers".

I second this. +1

5 hours ago, Andrew26 said:

What is infinity+i, infinity i+1 and infinity i+infinity?

i being the square root of -1 - the imaginary unit.

You might like to look at 'the point at infinity' in relation to complex numbers.

https://en.wikipedia.org/wiki/Riemann_sphere

[Country Boy]

Given an open line segment, say (a, b), there are two ways to "compactify" it.  One, the "Stone-Cech compactification", is to add the "endpoints", a and b, to get [a, b].  Another, the "one point compactification" is to imagine bending the line segment into a circle and adding a single point at the join.  Following those ideas, we can "compactify" the set of all real numbers by adding "+ infinity" and "- infinity"  or by adding a single point, "infinity", so that the topology becomes that of a circle,

Similarly here are two different ways to "compactify" the open disk, [tex]\{(x, y)| x^2+ y^2< r^2\}[/tex].  The "Stone-Cech compactification", by adding the points on the boundary to get [tex]\{(x, y)| x^2+ y^2= r^2\}[/tex], and the "one point compactification" where you bend the disk up into a sphere, adding a single point at the top.  

We can do the same thing with the set of all complex numbers, adding an infinite number of "points at infinity", one in every direction, or add a single "point at infinity".  In the first case the topology is that of a closed disk and in the second the topology is that of a sphere.

Edited November 18, 2019 by Country Boy