Mathematics Stack Exchange
Mathematics Stack Exchange

Questions tagged [proof-verification]

For questions concerning a specific proof or a specific solution, asking for verification, identifying errors, suggestions for improvement, etc. (You should not use this tag if the question does not contain a proposed proof/solution.)

For questions concerning a specific proof (or a proof sketch) or a solution to some problem; asking a question with this tag indicates one would like answers to respond broadly as to the following:

  • Verification of the proof/solution;
  • Identifying errors in the proof/solution;
  • Suggestions for improving the proof/solution;
  • Alternative approaches.

Also, consider the related tags and .

22798 questions
0
votes
0 answers

Little help with understanding a proof involving maxima,minima in a closed interval.

Here is an excerpt from Ross' Elementary Analysis Why did he let $|f(x_n)|>n$?
Oscar Flores
  • 1,438
  • 2
  • 18
  • 26
0
votes
0 answers

Check a new proof of Fermat's little theorem

Is my proof below original? We prove Fermat's little theorem in the reduced formulation: If $p$ is an odd prime and $a$ is an integer such that $p < a$ and $p \nmid a,$ then $a^{p-1} \equiv 1\ (mod\ p).$ Note, since $p$ is an odd prime, that the…
Yes
  • 20,719
-1
votes
1 answer

Proof by direct method?

Definition: An integer $n$ is throdd if $n=3k+1$ for some $k\in\Bbb Z$. Proposition: For all integers $n$, if $n^2$ is throdd, then $n$ is throdd. direct proof: let $n$ be a particular but arbitrarily chosen throdd integer then $n = 3k + 1$ for…
John
  • 61
-1
votes
2 answers

show that $a(1-b)$ and $b(1-a)$ can not both be greater than 1/4 for any two $a,b \in \mathbb{N}$

Please help me solve this problem: show that $a(1-b)$ and $b(1-a)$ can not both be greater than 1/4 for any two $a,b \in \mathbb{N}$.
Enoch Nene Attamah
  • 3
  • 1
-1
votes
5 answers

Is my proof of $\sqrt{2} + \sqrt{3} + \sqrt{5}$ is an irrational number valid?

The question is prove $\sqrt{2} + \sqrt{3} + \sqrt{5}$ is an irrational number. I started by assuming the opposite that $\sqrt{2} + \sqrt{3} + \sqrt{5}$ is a rational number. I stated that a rational number is a number made by dividing two…
mathguy21
  • 21
  • 3
-1
votes
1 answer

Could some one help me about this proof? it is about closure.

Let E ⊆ R be nonempty and bounded above, and define s = sup(E). Show that s ∈the closure of E.
Zibo Hong
  • 1
-1
votes
4 answers

Determine the image of a function using **induction**

Question: Let $f:{\mathbb{R}}\rightarrow{\mathbb{R}}$ by $x \mapsto x^2 + 4x + 7.$ Without using Calculus, show that $Im(f) = [3,\infty)$. I believe I should prove this by induction, but I'm not sure where to go from there. Thanks. Attempt 0: We…
Dakota Grusak
  • 1
  • 3
-1
votes
2 answers

"Proof" that $i=-\sqrt3/3$

I encountered the following "proof" and I simply can't find the error in the reasoning. $$ e^{\frac{i\pi}{2}}=\cos{\frac{\pi}{2}} + i\sin{\frac{\pi}{2}} = i $$ $$ e^{\frac{i\pi}{6}}=\cos{\frac{\pi}{6}} +…
David Tonderski
  • 3
-1
votes
2 answers

Geometric sequence - Find the value at n years

If the value of a $2000 machine depreciates by 20% at the end of each year, what is its value at the end of 12 years? I just need help with the ratio, is -0.2 correct? Thank you.
shhh
  • 35
-1
votes
1 answer

Claim. Let $A_k$ be a countable set for each real number $k$. Then $\bigcup_{k \in \mathbb{R}} A_k$ is countable. Prove or Disprove

CounterExample: Let $A_k = \{k\}$, then Union of all $k$ $= \mathbb{R}$, and $\mathbb{R}$ is uncountable. Is this a valid counter example?
piza25
  • 68
-1
votes
1 answer

Polynomial expression proof

I have been trying to solve this proof posted on my timeline but I am stuck - I am not a mathematician but computer scientist, and I could do with some hints or on what attack to take or rules that would help me do it for myself.Proofs are my…
pythonMan
  • 109
-1
votes
1 answer

Hi, I'm wondering if someone can help me prove that if f is strictly monotone, then f is injective?

I'm wondering if someone can help me prove that if f is strictly monotone, then f is injective?
user433284
  • 3
-1
votes
3 answers

Where is the flaw in my reasoning?

I have developed a proof that contradicts the infinite-ness of $\infty$. Here is my proof: Let $a$ be equal to $0.00000000000...001$, where there are $\infty$ number of zeroes. We can also say $a$ is the first real number. Let $b$ be equal to…
InitializeSahib
  • 101
-1
votes
2 answers

Prove that there is a number that is exactly one more than its cube

Proof Let x be any real number then the statement: P: $x^3=x^3+1$ $\frac{x^3}{x^3} = \frac{x^3}{x^3}+\frac{1}{x^3}$ $1=1+\frac{1}{x^3}$ this equation has no solutions since $\frac{1}{x^3}$ can never equal 0 and is undefined when x=0. There fore P…
K. Gibson
  • 2,381
-1
votes
1 answer

New to proofs and need verification i started my proof correctly?

prove that if n,m are natural numbers and nm is even, then either n is even or m is even. Proof: Assume n,m are natural numbers and nm is even, then either n or m is even. Case 1: Assume n,m are natual numbers and nm is even, then n and m are even…
Christian Soto
  • 1
1 2 3
…
36
37