User Surb

111 votes

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Gradient of 2-norm squared

answered Jul 30, 2014 at 20:52

64 votes

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What is the "topology induced by a metric"?

answered Aug 25, 2015 at 22:39

48 votes

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Difference between sum and direct sum

answered Feb 24, 2015 at 14:52

46 votes

Possible number of open sets in a topology

answered Nov 4, 2023 at 17:22

38 votes

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Can you complete the expression $2 \underline{ }\, \underline{ }\, \underline{ } \,\underline{ } 5 = 2015$?

answered Aug 4, 2015 at 8:50

29 votes

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How would you count a base $> 36$ system?

answered Jul 1, 2014 at 16:26

21 votes

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Why $e^x$ never equal $x$?

answered Jun 30, 2014 at 21:07

20 votes

What is the gradient with respect to a vector $\mathbf x$?

answered Oct 6, 2015 at 9:05

19 votes

Find $x,y,z>0$ such that $x+y+z=1$ and $x^2+y^2+z^2$ is minimal

answered Dec 12, 2015 at 16:44

18 votes

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A certain kind of non-linear mapping from $\mathbb{R}^2$ to $\mathbb{R}^2$

answered Mar 9, 2017 at 23:33

18 votes

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The Absolute Value in the Integral of $1/x$

answered Aug 25, 2014 at 8:31

17 votes

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Prove that if $a,b \in \mathbb{R}$ and $|a-b|\lt 5$, then $|b|\lt|a|+5.$

answered Jun 30, 2015 at 13:06

16 votes

Notation: Vector contains an element equal to 0

answered Mar 28, 2018 at 14:02

15 votes

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Proof that the continuous image of a compact set is compact

answered Jul 21, 2014 at 19:54

15 votes

Ways to write "50"

answered Dec 10, 2014 at 21:59

14 votes

Is $\ln(x)$ ever greater than $x$?

answered Jun 25, 2014 at 12:47

14 votes

Show a matrix is invertible

answered Feb 25, 2015 at 11:59

14 votes

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Irrationality of $\sqrt[n]2$

answered Mar 15, 2015 at 18:26

14 votes

Norm induced by convex, open, symmetric, bounded set in $\Bbb R^n$.

answered Jan 3, 2017 at 9:33

13 votes

How to prove the formula for the residue of $f$ at a pole of order $m$?

answered Oct 14, 2015 at 20:13

13 votes

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Show that $f(x) = x^2$ is not uniformly continuous on $[0,\infty)$

answered Jun 26, 2015 at 20:30

13 votes

Continuous function satisfying $ f\left(\dfrac{x+t}{2}\right) \le f(x) + f(t)$ inequality must be $0$

answered Oct 26, 2022 at 9:51

12 votes

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Injective function from $\mathbb{R}^2 \to \mathbb{R}^2$ is surjective

answered Aug 19, 2017 at 19:01

12 votes

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prove geometrically that $\cos(a+b)=\cos(a)\cos(b)-\sin(a)\sin(b)$

answered Oct 1, 2015 at 11:46

12 votes

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Don't understand proof that interior of a set is open

answered Feb 25, 2015 at 14:08

12 votes

How to show that $f(x)=1/x^2$ is uniformly continuous on $x\ge1$?

answered Oct 31, 2015 at 21:13

12 votes

Why $\mathbb Z_2\otimes_{\mathbb Z}\mathbb Z_3\cong \{0\}$?

answered Feb 12, 2017 at 18:08

11 votes

How many 1's can a regular 0,1-matrix contain?

answered May 11, 2015 at 8:23

11 votes

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how to show that $f(\mathbb C)$ is dense in $\mathbb C$?

answered Mar 21, 2015 at 23:57

11 votes

Differentiability of product/composition of function

answered Jul 4, 2014 at 16:12

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2,239 Answers

Gradient of 2-norm squared

What is the "topology induced by a metric"?

Difference between sum and direct sum

Possible number of open sets in a topology

Can you complete the expression $2 \underline{ }\, \underline{ }\, \underline{ } \,\underline{ } 5 = 2015$?

How would you count a base $> 36$ system?

Why $e^x$ never equal $x$?

What is the gradient with respect to a vector $\mathbf x$?

Find $x,y,z>0$ such that $x+y+z=1$ and $x^2+y^2+z^2$ is minimal

A certain kind of non-linear mapping from $\mathbb{R}^2$ to $\mathbb{R}^2$

The Absolute Value in the Integral of $1/x$

Prove that if $a,b \in \mathbb{R}$ and $|a-b|\lt 5$, then $|b|\lt|a|+5.$

Notation: Vector contains an element equal to 0

Proof that the continuous image of a compact set is compact

Ways to write "50"

Is $\ln(x)$ ever greater than $x$?

Show a matrix is invertible

Irrationality of $\sqrt[n]2$

Norm induced by convex, open, symmetric, bounded set in $\Bbb R^n$.

How to prove the formula for the residue of $f$ at a pole of order $m$?

Show that $f(x) = x^2$ is not uniformly continuous on $[0,\infty)$

Continuous function satisfying $ f\left(\dfrac{x+t}{2}\right) \le f(x) + f(t)$ inequality must be $0$

Injective function from $\mathbb{R}^2 \to \mathbb{R}^2$ is surjective

prove geometrically that $\cos(a+b)=\cos(a)\cos(b)-\sin(a)\sin(b)$

Don't understand proof that interior of a set is open

How to show that $f(x)=1/x^2$ is uniformly continuous on $x\ge1$?

Why $\mathbb Z_2\otimes_{\mathbb Z}\mathbb Z_3\cong \{0\}$?

How many 1's can a regular 0,1-matrix contain?

how to show that $f(\mathbb C)$ is dense in $\mathbb C$?

Differentiability of product/composition of function