# Recent content by CaptainAmerica17

1. ### I Help Finding the Correct Approach to this Proof (Intro Real Analysis)

This is great! I can use this as a reference for future problems as well, thank you!
2. ### I Help Finding the Correct Approach to this Proof (Intro Real Analysis)

Honestly thinking about things in this way really helps I can tell the difference. When I do proof problems from my linear algebra book, it normally doesn't take much time at all because everything seems much more straightforward. The thinking for these kinds of proofs just seems different for...
3. ### I Help Finding the Correct Approach to this Proof (Intro Real Analysis)

No worries! All of this is very helpful. I think I just need to stick it out for the simpler stuff, but also not be afraid to move along when necessary. The thing you said about definitions is something that has tripped me up more than once, no one has ever pointed it out to me before now.
4. ### I Help Finding the Correct Approach to this Proof (Intro Real Analysis)

Thanks for the advice! I don't know why I always feel the need to do every single part of a textbook. Just recently, someone told me that they normally only do half of the problems in a textbook. I had spent weeks doing every problem in every section of the books I'm working on and was wondering...
5. ### I Help Finding the Correct Approach to this Proof (Intro Real Analysis)

No this is like set theory stuff. In the book I'm using, the "real" stuff comes after set theory and properties of the real numbers. Most of the problems are just proofs of definitions similar to this. I've thought about skipping it multiple times but decided against it. I'm starting a degree in...
6. ### I Help Finding the Correct Approach to this Proof (Intro Real Analysis)

Yes, that is the definition I am using. I'll give this approach some thought. Thanks for the response!
7. ### I Help Finding the Correct Approach to this Proof (Intro Real Analysis)

Ok, so here is what I have so far: Suppose ##T_1## is infinite and ##\varphi : T_1 \rightarrow T_2## is a bijection. Reasoning: I'm thinking I would then show that there is a bijection, which would be a contradiction since an infinite set couldn't possibly have a one-to-one correspondence...

Lol
9. ### I Proof about injectivity

Let ##y \in E##. Assume that ##f## is surjective. There is some ##x \in f^{-1}(E)## such that ##y = f(x)##. So by definition, ##x =f(x) \in f(f^{-1}(E))##. At least I finally got something understandable. I didn't have nearly as much trouble proving things about inverse images themselves (i.e...
10. ### I Proof about injectivity

Thank you for this. It took a while to reply because I had to get caught up on some school work. Here's what I worked out: If ##y \in f(f^{-1}(E))##, then ##y = f(x)## for some ##x \in f^{-1}(E)##. So if you have ##x \in f(f^{-1}(E))##, you have it will clearly map back to the set ##E##. So we...
11. ### I Proof about injectivity

Thank you for this. It took a while to reply because I had to get caught up on some school work. Here's what I worked out: If ##y \in E##, then ##y = f(x)## for some ##x \in f^{-1}(E)##. Clearly, ##f^{-1}(E)## is the set of all points that map into ##E##, so ##f(f^{-1}(E))## will give us all...
12. ### I Proof about injectivity

ok, I've thought about it about. The goal of this proof should be to show that ##y \in f(f^{-1}(E) \iff y \in E## So to start with ##y \in f(f^{-1}(E)##. ##y = f(x)## for some ##x \in f^{-1}(E)## Or maybe since it is surjective, it is best to start with ##y \in E## so that we can show that...
13. ### I Proof about injectivity

Ah, ok. I was drawing out a picture and it wasn't making sense.
14. ### I Proof about injectivity

E is a subset of A or B?
15. ### I Proof about injectivity

Wow, I really overcomplicated things XD