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5h
comment Inverse of a set, possible?
I don't know where you're going there. Notions of negative cardinality don't on the face it appear very useful.
5h
answered Inverse of a set, possible?
5h
reviewed Leave Open Is there any construction method that yields all algebraic numbers?
5h
reviewed Leave Open Transformation matrix between 2 bases
5h
reviewed Leave Open Stone-Weierstrass: Examples
5h
reviewed Close What is some pure math news website by a publisher?
8h
reviewed Approve Why is this function an embedding?
10h
comment Proving $\lim_{x\to9}\sqrt x=3$ using Cauchy's definition
I don't think you can. I'd look again at the choice of $\delta$.
10h
reviewed Approve Proof of the properties of tensor product
10h
answered Differential Geometry
10h
comment Differential Geometry
If $x' = f(x,y)$ and $y' = g(x,y)$, then $dx' = f_x dx + f_y dy$ and $dy' = ...$; hence $dx \wedge dy = ...$
11h
comment Differential Geometry
Have you tried just to write it out? Follow your nose and I think you'll find it very clear.
1d
reviewed Approve Problem understanding the Axiom of Foundation
1d
comment Using $\epsilon$ and $\delta$ to prove that $\lim_{x \to 0}\frac{\tan x}{x}=1$
You've already given too much away with your inequality. How can you make this smaller than $\epsilon$ with that stubborn $1$ there? Try another factoring and remember $(\sin x)/x \to 1$
1d
comment How to prove this equation by induction?
Have you tried writing out $f_{n+2}f_n$ ... how far have you got by yourself?
2d
answered Inverse Laplace of $\frac 1 {(s^2+a^2)^n}$
2d
comment Summation notation confusion in the Cauchy-Schwarz Master Class book
Yes. The tacit convention is that when a summation is given it ranges over all valid values of the index variable(s), $j$ in this case.
2d
comment Summation notation confusion in the Cauchy-Schwarz Master Class book
"Does that mean that it is the sum of all the terms in the sequence". Yes
2d
comment Surface area of a solid of revolution: Why does not $ \int_{b}^{a} 2\pi \,f(x) \,dx $ work?
It's worth going back to the Riemann sums in both cases to make sure you understand how the SA and volume integrals are constructed.
2d
comment Surface area of a solid of revolution: Why does not $ \int_{b}^{a} 2\pi \,f(x) \,dx $ work?
Because in the volume calculation you are adding up 'discs' of cross-sectional area $\pi f(x)^2$ and width $dx$. There no sort of adjustment is required.