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Feb
4
comment Equation of normal vector pointing away from ellipse
As @YvesDaoust said. Usually, the slope that you quoted, is derived from that formula, not the other way around. Also, a note on terminology: The gradient is usually a vector. What you called gradient in the question should be called slope. (Though in everyday language, the two are often taken to be the same.)
Feb
4
comment Equation of normal vector pointing away from ellipse
I fixed a typo for you, replacing an $x$ by $y$ in the formula for the ellipse.
Feb
4
revised Equation of normal vector pointing away from ellipse
Fixed presumed typo
Feb
4
comment Convolution and absolute value
@sunrise $y$ is the integration variable that ranges over the intervals I mention in the bullet list. See the edit, it should explain it fully.
Feb
4
revised Convolution and absolute value
Elaborate
Feb
3
answered Convolution and absolute value
Feb
3
revised Convolution and absolute value
Fixed latex problem
Feb
3
comment Is it true that GCD$(\alpha,b)=1$?
@PedroSánchezTerraf yes, but those are $\alpha$ and $\beta$. The question is about $\alpha$ and $b$. (Unless it's a typo, in which case I answered the wrong question.)
Feb
3
answered Is it true that GCD$(\alpha,b)=1$?
Jan
31
awarded  Good Answer
Jan
28
comment analytic solution of a definite integral
Surely, this cries out for subsituting $u=(1+x^c)^k-1$, does it not?
Jan
28
comment analytic solution of a definite integral
Under no circumstance use asterisks for multiplication (except in computer programming, where you don't have any other choice, of course). In mathematics, it most commonly denotes convolution, which is another type of beast entirely. If you need a multiplication sign, use \cdot ($\cdot$) instead.
Jan
27
comment Is every shape possible with a snake?
@Lembik I see. That's good.
Jan
27
comment Is every shape possible with a snake?
@Lembik I don't mind. But it is common to give credit when you use other people's work this way, say by linking here. I don't really care if you do in this case, but if it were the result of a bigger effort, I might care. So to play it safe, you should get into the habit of providing that link.
Jan
27
comment Is every shape possible with a snake?
@Lembik If it does, then the head will touch the adjacent bit of snake, right? I had assumed this was disallowed. If it is allowed, then you're right, but that is the only thing you can do. Of course, if a 180° turn is allowed, so a length of snake is on top of the adjacent length, then any shape is trivially reachable, since the snake can just roll itself up into a single segment and the unroll itself into the required shape.
Jan
27
comment Is every shape possible with a snake?
@hardmath Ah well, I fixed it with some unicode box art. Unfortunately, there is a small gap between the text lines which makes breaks in the vertical lines, but it can't be helped.
Jan
27
revised Is every shape possible with a snake?
ASCII to unicode
Jan
27
comment Is every shape possible with a snake?
@hardmath Indeed. If I had deleted the four seemingly redundant text lines, I would end up with an ambiguous looking stack of three pluses on the right margin. I could probably have done better if I looked up the line art characters that exist somewhere in unicode land, though.
Jan
27
answered Is every shape possible with a snake?
Jan
26
comment Prove that $2^{3^n} + 1$ is divisible by 9, for $n\ge1$
I fixed the formatting for you. But please, please, do provide some context and tell us what you tried.