• Yesterday, 17:22
I believe that it should be: \begin{align*}\frac{\partial}{\partial{t}}f(x+c(t-\tau ),\tau)&=f_x(x+c(t-\tau ),\tau)\cdot...
11 replies | 152 view(s)
• Yesterday, 14:06
I think this is correct yes. (Nod) And we can simplify it bit more since $f(y,\tau)$ does not depend on $t$. Therefore $\pd{}t f(y,\tau)=0$....
11 replies | 152 view(s)
• Yesterday, 06:39
I am reading T. S. Blyth's book: Module Theory: An Approach to Linear Algebra ... I am focused on Chapter 2: Submodules; intersections and sums...
0 replies | 32 view(s)
• Yesterday, 03:00
In Chapter 1 of his book: "Modules and Rings", John Dauns (on page 7) considers a subset T of an R-module M and defines the R-submodule generated by...
0 replies | 35 view(s)
• Yesterday, 00:27
Hi steenis ... despite your help (thank you) ... I have not been able to make much progress on the converse ... see below ... Converse: ...
14 replies | 240 view(s)
• May 24th, 2018, 16:06
Ah okay. My mistake. (Blush) So we have: \begin{tikzpicture} \coordinate (A) at (-1,0); \coordinate (B) at (1,0); \coordinate (C) at...
6 replies | 86 view(s)
• May 24th, 2018, 16:00
MarkFL replied to a thread Word problem on vectors in Geometry
Hello, and welcome to MHB, Gummg! (Wave) I would write the plane's velocity vector as: \vec{v}=485\left\langle...
3 replies | 78 view(s)
• May 24th, 2018, 15:38
Brainstorming some more, I believe we are approximating $y(x)$ with its Fourier form, which is: $$y(x) \approx \sum_{j=1}^{n-1} a_j \sin(jx)$$ It...
2 replies | 70 view(s)
• May 24th, 2018, 15:16
Because: \begin{tikzpicture} \coordinate (A) at (-1,0); \coordinate (B) at (1,0); \coordinate (C) at (0,{sqrt(3)}); \coordinate (D) at...
6 replies | 86 view(s)
• May 24th, 2018, 14:18
Hi ion88, welcome to MHB! (Wave) No worries. I believe you've already correctly filled in the table, which is what MarkFL uploaded for you. ...
4 replies | 97 view(s)
• May 24th, 2018, 14:06
Can it be that it should be side length $2b$ and height $a$? (Wondering) I don't think $AFA_1$ is equilateral. And $A_1$ is not in the...
6 replies | 86 view(s)
• May 24th, 2018, 11:48
STANDARD formula (google would have given it to you Mr.Fly!): P = Ai / (1-v) where v = 1 / (1+i)^n (same as TK's) P = ? A = 2,000,000 i = .10...
8 replies | 135 view(s)
• May 24th, 2018, 10:27
Hey mathmari!! (Wave) It seems to me that the matrix indeed comes from the finite differences method. It identifies the problem that we want to...
2 replies | 70 view(s)
• May 23rd, 2018, 17:20
I assume a theory $T$ is called effectively axiomatized if its set of axioms is decidable. (The following argument does not change if the set of...
2 replies | 61 view(s)
• May 23rd, 2018, 14:46
I think it should be $f(y,t)$ and $f_t(y,t)$, shouldn't it? Otherwise I believe it's all correct. (Happy)
11 replies | 152 view(s)
• May 23rd, 2018, 11:43
Here is this week's POTW: ----- Prove that there are only a finite number of possibilities for the ordered triple $(a-b,\,b-c,\,c-a)$ where...
0 replies | 67 view(s)
• May 23rd, 2018, 11:40
Congratulations to the following members for their correct solution:): 1. Olinguito 2. Opalg Solution from Opalg: If...
1 replies | 104 view(s)
• May 23rd, 2018, 10:55
If $\phi(x)\ne 0$ then we must have that $x\le \beta$ yes? And $\beta \le |\beta| \le \max(|\alpha|,|\beta|)$ isn't it? So if $\phi(x)\ne 0$ then...
19 replies | 298 view(s)
• May 23rd, 2018, 10:44
How does this follow? That's what I don't understand... (Worried)
19 replies | 298 view(s)
• May 23rd, 2018, 10:39
Suppose $\phi(x)=0$ for $x\in \mathbb R \setminus$. Then that means that we have that $\phi(x)=0$ for $x >\max(|\alpha|,|\beta|)$ don't we? And...
19 replies | 298 view(s)
• May 23rd, 2018, 10:18
I am a little confused right now. Could you explain to me why this holds? (Worried)
19 replies | 298 view(s)
• May 23rd, 2018, 10:16
Hey mathmari!! (Wave) How about defining $g(x,t,\tau) = \int_{c(t-\tau)-x}^{x+c(t-\tau)}f(y,\tau)dy$, and then differentiating one integral at a...
11 replies | 152 view(s)
• May 23rd, 2018, 10:05
How about picking $L= \max(|\alpha|, |\beta|, |\gamma|, |\delta|)$? Then $\phi=\psi=0$ on $\mathbb R\setminus$ isn't it? (Wondering) Btw, we...
19 replies | 298 view(s)
• May 23rd, 2018, 08:41
No, I am wrong.... Because if we have $\phi(x)=0$ for $x \in \mathbb{R} \setminus{}$, it doesn't imply that $\phi(x)=0$ for $x \in \mathbb{R}... 19 replies | 298 view(s) • May 23rd, 2018, 08:29 The closed and bounded sets where the functions are non-zero don't have to be of the form$$, do they? But are we sure that the sets are in the form... 19 replies | 298 view(s) • May 23rd, 2018, 07:55 Now consider \phi \ : \ M^{(\Delta)} = \bigoplus_\Delta M_\alpha \to N Let ( x_\alpha ) \in \bigoplus_\Delta M_\alpha ... Then by... 14 replies | 240 view(s) • May 23rd, 2018, 07:01 Thanks ... OK now ... Peter 14 replies | 240 view(s) • May 23rd, 2018, 06:47 Thanks again steenis ... ... But ... just a clarification ...$f \neq 0$, so there is a$y \in N$with$f(x) \neq 0$. ... ... " Did you... 14 replies | 240 view(s) • May 23rd, 2018, 06:27 Can't we take the union of those 2 bounded sets? That is, pick$L$such that it's bigger than any$x$-value for which either$\phi(|x|)$or... 19 replies | 298 view(s) • May 23rd, 2018, 06:15 Thanks steenis ... Reflecting on your advice now ... Peter 14 replies | 240 view(s) • May 23rd, 2018, 05:58 I am thinking about it again now. Couldn't it be that the bounded set where$\phi$is non-zero and the bounded set where$\psi$is non-zero are... 19 replies | 298 view(s) • May 23rd, 2018, 04:39 I found that there's usually a pattern to these exercises. The first series are usually questions about the words, symbols, and definitions that... 14 replies | 326 view(s) • May 23rd, 2018, 04:27 I just realized that there is yet another notation. What if we write$f=f(\cdot)$? That is correct (i.e. equivalent) without ambiguity isn't it?... 14 replies | 326 view(s) • May 23rd, 2018, 02:54 All correct. (Happy) 19 replies | 298 view(s) • May 23rd, 2018, 01:59 Ah I see... In order$\int_{x-cT}^{x+cT}\psi(\tau)d\tau$to be zero, there are two possible cases: either$x-cT<-L \Rightarrow x<cT-L\$ and...
19 replies | 298 view(s)
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"It's not necessary for you to pick pen and paper to solve a problem, the most intriguing questions are those that you're thinking of most of the time anyway" Zaid Alyafey .

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