/sci/ - Science & Math

So I saw this and I'm thinking about infinity.

If .9...=1, then wouldn't .8...9... (That's .8 repeating infinitely followed by 9 repeating infinitely.) equal .8...9, meaning that it would be turning an infinite number finite. And then wouldn't this mean that it's actually subtracting an infinite amount since the end result is infinitely smaller than the starting amount? Like, can you have multiple infinities, or is it just infinity as a concept at that point? But then wouldn't that mean all infinities are equal, which would make all numbers equal if this picture is true? Where do I start learning about infinity? Is infinity, like, a waveform that collapses once it's interacted with?