User graydad

35 votes

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

answered May 17, 2015 at 18:49

29 votes

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

answered Oct 9, 2014 at 17:32

19 votes

Accepted

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

answered Mar 25, 2015 at 15:14

17 votes

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

answered Jun 24, 2015 at 15:30

13 votes

Accepted

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

answered Feb 23, 2015 at 17:10

12 votes

Accepted

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

answered Feb 20, 2015 at 23:56

12 votes

Chain rule with triple composition

answered Nov 14, 2014 at 15:35

11 votes

What to answer when people ask what I do in mathematics

answered Feb 8, 2015 at 18:56

11 votes

Accepted

Doubt about the domain in logarithmic functions.

answered May 26, 2015 at 15:05

10 votes

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

answered Oct 11, 2015 at 16:36

9 votes

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

answered Mar 9, 2015 at 20:46

9 votes

Accepted

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

answered Aug 27, 2014 at 18:02

9 votes

Accepted

subtracting inequalities if difference is positive

answered Jun 14, 2015 at 17:00

8 votes

Accepted

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

answered Feb 24, 2015 at 15:21

8 votes

Accepted

Roots of a cubic

answered Mar 23, 2015 at 18:16

7 votes

Accepted

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

answered Aug 17, 2014 at 20:45

7 votes

Accepted

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

answered Oct 5, 2014 at 21:18

7 votes

Accepted

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

answered Nov 5, 2014 at 5:48

7 votes

Accepted

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

answered Jun 11, 2015 at 14:38

6 votes

Accepted

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

answered Nov 18, 2014 at 19:00

6 votes

Accepted

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

answered Dec 3, 2014 at 19:26

6 votes

Accepted

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

answered Jun 4, 2015 at 18:35

6 votes

Accepted

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

answered May 8, 2015 at 20:56

6 votes

Accepted

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

answered Jun 25, 2015 at 2:48

6 votes

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

answered Jul 1, 2015 at 14:46

6 votes

Accepted

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

answered Oct 8, 2015 at 6:01

5 votes

Accepted

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

answered Mar 28, 2015 at 17:27

5 votes

Accepted

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

answered Mar 2, 2015 at 17:28

5 votes

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

answered Feb 4, 2015 at 17:15

5 votes

Solve the equation $4^{7 x - 10} = 10^{7 x - 6}$ for $x$

answered Oct 5, 2014 at 22:34

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603 Answers

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

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

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

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

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

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

Chain rule with triple composition

What to answer when people ask what I do in mathematics

Doubt about the domain in logarithmic functions.

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

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

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

subtracting inequalities if difference is positive

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

Roots of a cubic

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Solve the equation $4^{7 x - 10} = 10^{7 x - 6}$ for $x$