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seen Dec 7 at 21:45

Dec
20
comment Finding the number of points on the straight line joining $(-4,11)$ and $(16,-1)$
@ShaneORourke: oh don't worry, I know how to find the answer, but clearly something's missing.
Dec
20
comment Finding the number of points on the straight line joining $(-4,11)$ and $(16,-1)$
How did you find these solutions? Why aren't there more? This is an incomplete answer.
Dec
17
comment Can't argue with success? Looking for “bad math” that “gets away with it”
Unfortunately, this is almost literally how Cayley-Hamilton is proved in Stoll's syllabus on linear algebra (see Theorem 2.1): math.leidenuniv.nl/~desmit/edu/la2_2012/LinAlg2-index.pdf
Dec
17
comment Question involving entire functions
@pankaj: you don't need to be "sorry". just read up on the identity theorem, and ask us about that instead of trying to answer these questions.
Dec
17
comment Question involving entire functions
There's hardly anything to add without giving the answer away at this stage.
Dec
17
comment Question involving entire functions
If you are still not getting it, you don't know the identity theorem.
Dec
17
comment Question involving entire functions
Dear pankaj, you have now asked three questions, all of which show no own work. Try investing a little time in the material before you come to us, and if you had any thoughts, please tell us what you've tried.
Dec
17
comment boundedness of an operator
$\frac{f(x)}{1+|x|+|y|}\leq f(x)$
Dec
17
comment Show the function $x_1\sin(1/x_2)+x_2\sin(1/x_1)$ is continuous everywhere
Okay, so $\lim_{x\to1}F(x,x-1)-(x-1)\sin(1/x)$ should be defined by continuity of F and convergence of the term $(x-1)\sin(1/x)$ (convergence because $x-1\to0$ and $\sin$ is bounded). But this limit is your $x\sin(\frac{1}{x-1})$, which indeed does not converge since $\frac{1}{x-1}$ does not (add a few sentences here), ergo $F$ is not continuous.
Dec
17
comment Show the function $x_1\sin(1/x_2)+x_2\sin(1/x_1)$ is continuous everywhere
I don't know, your reasoning sounds alright but you'll need to add a sentence somewhere - I'm not quite convinced.
Dec
17
comment Show the function $x_1\sin(1/x_2)+x_2\sin(1/x_1)$ is continuous everywhere
The fact that your calculations do not work does not prove $F$ cannot be continuously defined. In particular, the fact that the individual limits do not exist does not prove that the sum does not (for example, consider $0=\lim 1/x - 1/x=\lim1/x-\lim1/x$).
Dec
17
comment Displaying $2 \cdot 10^5$ as $200000$
Right click on the result, Numeric formatting.
Dec
17
comment Prove that $\int_0^{+\infty} \frac{\ln x}{a^2+x^2} dx = \frac{\pi\ln a}{2a}$
Perhaps this is not an answer for Leitingok, but this is exactly how they would do it in the book, and shows the power of complex analysis. +1.
Dec
17
comment Given joint pdf of $X$ & $Y$, find pdf $Z=XY$
Yes. $X\leq1$ and $Y\leq1$ so $Z=XY\leq1$.
Dec
16
comment $f^{-1}$ and continuity
This is actually one of the definitions for continuity, so you really need to explain what definition you are using.
Dec
16
comment linear hyperbolic PDE with some BCs at infinity
Hello there, try putting your equations in latex, as explained here: meta.math.stackexchange.com/questions/107/…
Dec
16
comment Prove that $f'$ exists for all $x$ in $R$
You make quite a stronger statement than what was asked for, but it's technically correct.
Dec
16
comment Complex Functions Concept Questions
I think the fact that these answers are longer than the normal, mathematical, equation-rich answers, says enough about this method of teaching.
Dec
16
comment Prove that $f'$ exists for all $x$ in $R$
Related: math.stackexchange.com/questions/151032/…
Dec
16
comment Prove that $f'$ exists for all $x$ in $R$
Related: math.stackexchange.com/questions/175607/…