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graydad
  • Member for 9 years, 11 months
  • Last seen more than 1 year ago
35 votes

What's wrong with l'Hopital's rule?

29 votes

What is an example of function $f: \Bbb{N} \to \Bbb{Z}$ that is a bijection?

20 votes
Accepted

Why/How does this sqrt term work? The inverse of a fraction in a sqrt

17 votes

Easy math proofs or visual examples to make high school students enthusiastic about math

13 votes
Accepted

Proof: The identity matrix is invertible and the inverse of the identity is the identity

12 votes
Accepted

How do I determine if a set is open or closed??

12 votes

Chain rule with triple composition

11 votes

What to answer when people ask what I do in mathematics

11 votes
Accepted

Doubt about the domain in logarithmic functions.

10 votes

The coefficient of $x^9$ in the expansion of $(1+x)(1+x^2)(1+x^3)\cdots(1+x^{100})?$

10 votes

Why is $-5^2=-25$?

9 votes
Accepted

subtracting inequalities if difference is positive

9 votes
Accepted

Why is the cube-root of $x$ 'odd'?

8 votes
Accepted

If $e^{i\theta}=e^{i\varphi}$, then $\theta-\varphi=2k\pi$

8 votes
Accepted

Roots of a cubic

7 votes
Accepted

Integrate $ \int \frac{x^2}{x+1} dx $

7 votes
Accepted

Find the number of positive integers solutions of the equation $3x+2y=37$

7 votes
Accepted

Even and odd proof - if n is even then $n^{2} -1$ is odd.

7 votes
Accepted

How to solve $z^6+i=0$

7 votes
Accepted

If $a$ and $b$ are positive real numbers, then $a + b \geq 2 \sqrt{ab}$.

6 votes
Accepted

Why is this limit $\lim_{n \to \infty}(1 + \frac{1}{n})^n$ equal to $e$?

6 votes
Accepted

How to prove $\sqrt\frac{1 - \sin x}{1 + \sin x} = \frac{1}{\cos x} - \tan x$

6 votes
Accepted

When I prove two topologies are same, is it sufficient to prove they have same basis? If so,Why?

6 votes

why $ \sum_{k=0}^{\infty} x^{2k} = \frac{1}{1-x^2}\\$

6 votes
Accepted

Find an increasing sequence of rationals that converges to $\pi$

6 votes
Accepted

Prove A is an open set if and only if $A \cap Bd(A) = \emptyset $

5 votes
Accepted

Does this series $\sum_{i=0}^n \frac{4}{3^n}$ diverge or converge?

5 votes
Accepted

About the divergence of $\sum^\infty_{n=1}\frac 1 {n\cdot n^{1/n}}$

5 votes

An example of an infinite open cover of the interval (0,1) that has no finite subcover

5 votes

How to integrate $\int (x-1)\sqrt{x} \, \text{d}x$

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