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MathMathCookie
  • Member for 12 years, 1 month
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46 votes
6 answers
5k views

Why do we write proofs "forward?"

23 votes
2 answers
6k views

Interpreting the significance of Darboux's Theorem

18 votes
2 answers
42k views

How to prove $\sin(1/x)$ is not uniformly continuous

16 votes
3 answers
14k views

Example of a function that is not twice differentiable

11 votes
2 answers
2k views

Countable or uncountable set 8 signs

8 votes
4 answers
9k views

Proof: If $f'=0$ then is $f$ is constant

7 votes
3 answers
377 views

Wrong Definition of a Limit

7 votes
1 answer
764 views

Lipschitz at every point in $[a,b]$ but not Lipschitz on $[a,b]$?

7 votes
2 answers
17k views

Prove the integral of $f$ is positive if $f ≥ 0$, $f$ continuous at $x_0$ and $f(x_0)>0$

5 votes
1 answer
195 views

Is this proof wrong?

5 votes
2 answers
1k views

Variant on Bayes's Rule and weather forecasting

4 votes
3 answers
2k views

Proof for Integral Inequality $|\int f| \le \int |f|$ - is it sufficient enough?

3 votes
4 answers
2k views

What's wrong with my epsilon delta proof here?

3 votes
1 answer
4k views

Showing Linear Independence $\{1,\sin x,\cos x\}$

3 votes
1 answer
13k views

What does it mean for a functional equation to have a unique solution?

3 votes
3 answers
346 views

Solving the equation $f(x+t)=f(x)+f(t)+2\sqrt{f(x)}\sqrt{f(t)}$

2 votes
3 answers
663 views

Finding the number of edges that connect to a single vertex in a dodecahedron

2 votes
1 answer
2k views

Showing $\sin(1/x)$ is not a rectifiable curve

2 votes
1 answer
983 views

Proof of the following fact: $f$ is integrable, $U(f,\mathcal{P})-L(f,\mathcal{P})<\varepsilon$ for any $\varepsilon>0$

2 votes
1 answer
115 views

How should one prove: $\lim_{x\to a}~ x^2 = a^2$? [Sketch of proof inside]

2 votes
2 answers
13k views

Is $f'$ continuous at $0$ if $f(x)=x^2\sin(1/x)$

2 votes
1 answer
2k views

Rigorous Proof?: Proving Cauchy Criterion of Integrals

2 votes
1 answer
780 views

If f is differentiable at a, then f is Lipschitz of order 1 at a

1 vote
1 answer
174 views

Example of functions $f$ and $g$ such that $g \circ f$ is not convex

1 vote
1 answer
2k views

Prove $\lim\limits_{x→∞} f''(x) = 0$

1 vote
1 answer
173 views

Quick Question Checking an example where inequality is strict

1 vote
4 answers
910 views

Finding all functions $f$ satisfying $f'(t)=f(t)+\int_a^bf(t)dt$

1 vote
1 answer
898 views

Need help understanding the proof of $\exp(x+y)=\exp(x)\exp(y)$

1 vote
5 answers
392 views

Solving an equation with absolute values

1 vote
1 answer
182 views

Does the infinite sum of $\frac{n+1}{\ln(n+1)}$ converge?