Christian Blatter

ETH Zurich (Switzerland)

math.ethz.ch/~blatter

Age: 79

3h
answered Can zero rows in matrices be ignored in calculations of matrix products?
4h
answered What is the minimum number of colours needed for coding 12 objects, if each may be marked with either one or two colours?
4h
comment What is the minimum number of colours needed for coding 12 objects, if each may be marked with either one or two colours?
It would be interesting to see the combinatorial reasoning behind this answer, which in the end is correct.
8h
answered Geometry of Metric Spaces
8h
answered Show that $e^{iy} = 1 + iy + \frac{\mu_1 y^2}{2}$ for all $y \in \mathbb{R}$ with $|\mu_1| \leq 1$
8h
revised Is $dx\,dy$ really a multiplication of $dx$ and $dy$?
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9h
revised How exactly do I prove that I find the maximum of the function
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10h
comment Show that the graph of $y=x^3\sin(\pi/x)$ extends to a smooth arc
@Savage Henry: See my edit. You don't have to define the derivative; you have to compute the derivative at $0$, using the definition of derivative.
10h
revised Show that the graph of $y=x^3\sin(\pi/x)$ extends to a smooth arc
added 260 characters in body
22h
answered Show that the graph of $y=x^3\sin(\pi/x)$ extends to a smooth arc
22h
answered Find the smallest positive number $p$ for which the equation $\cos(p\sin x)=\sin(p \cos x)$ has a solution $x\in[0,2\pi].$
1d
awarded Yearling
1d
comment When do evaluation and the integral sign "commute"?
There is no problem at all. You are given a function $f$ on some rectangle $[a,b]\times[p,q]$ and are considering the integral of $f$ along segments $y=c\in[p,q]$. The value of this integral is a function of the chosen "level" $c$ and can therefore be denoted by $g(c)$.
1d
comment Why do we still do symbolic math?
If you couldn't compute symbolically you'd never know what to compute numerically.
2d
revised Constructing a family of distinct curves with identical area and perimeter
added 500 characters in body
2d
answered Constructing a family of distinct curves with identical area and perimeter
2d
answered How exactly do I prove that I find the maximum of the function
2d
awarded Enlightened
2d
awarded Nice Answer
2d
revised Choosing 5 of 40 people sitting at a circular table so that between any two are at least three other people
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