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Jan
22
comment Subgroup of $\mathbb{Q}$ containing $\mathbb{Z}$
Do you take group w.r.t. to $+$ or $\times$?
Jan
22
comment How can you find $m$ in $mx^2+(m-3)x+1=0 $ so that there is only one solution
I don't think so and I give you +1; this approach is slightly different than in the other answers and shows a nice use of Vièta's formulas.
Jan
22
revised Number of Perfect Powers in Pascal`s Triangle
edited tags
Jan
22
comment Calculating $\lim_{n\to\infty}\sqrt[n]{ \sqrt[n]{n} - 1 }$
No, the OP did not do that, but it's easy, because $n^{1/n}>1$ for all $n$.
Jan
10
comment When does one consider the laplacian as a dirac delta function?
The direct calculation does not work at zero (the origin), which is where you're losing your delta function. It's similar to saying that the derivative of $x\mapsto|x|$ is the signum of $x$; you lose one point.
Jan
10
comment How many sequences of rational numbers converging to 1 are there?
Isn't simply $\mathbb{N}^\mathbb{N}$ a continuum, whence also $\mathbb{Q}^\mathbb{N}$ is?
Jan
10
answered How many sequences of rational numbers converging to 1 are there?
Dec
27
comment How can one determinate the variationt of $f(g(x))$
@user233658 Because $f$ is decreasing for arguments $<1$ and increasing for arguments $>1$.
Dec
26
revised How can one determinate the variationt of $f(g(x))$
edited tags
Dec
26
answered How can one determinate the variationt of $f(g(x))$
Dec
16
accepted Limit of $e^x/x^3$ at infinity without l'Hopital
Dec
16
comment Limit of $e^x/x^3$ at infinity without l'Hopital
mickep @Ian Oh I now realize the trick (sorry it's early in the morning here). That looks really nice, thanks!
Dec
16
comment Limit of $e^x/x^3$ at infinity without l'Hopital
@Ian Yes, I know. The problem is that this is for 1st year university students, and we tend to disallow using derivatives for limits at the beginning. And after one does what you do, it gets very complicated. Thanks for your help anyway!
Dec
16
comment Limit of $e^x/x^3$ at infinity without l'Hopital
@Ian If you ever write $y'$, you are quite obviously using derivatives.
Dec
16
comment Limit of $e^x/x^3$ at infinity without l'Hopital
@Ian How do you prove convexity?
Dec
16
comment Limit of $e^x/x^3$ at infinity without l'Hopital
I have exactly the problem @sranthrop speaks about. How do you prove that $e^t\geq t+1$ without taking derivatives?
Dec
16
revised Limit of $e^x/x^3$ at infinity without l'Hopital
added 54 characters in body
Dec
16
comment Limit of $e^x/x^3$ at infinity without l'Hopital
As $\lim (1+x/n)^n$, I'll include this.
Dec
16
revised Limit of $e^x/x^3$ at infinity without l'Hopital
edited title
Dec
16
asked Limit of $e^x/x^3$ at infinity without l'Hopital