Christian Blatter

ETH Zurich (Switzerland)

math.ethz.ch/~blatter

Age: 79

7h
revised Find the locus of points M the difference of the squares of whose distances from two given points A and B is equal to a given value c.
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7h
revised Invent transformation mapping ellipsoid to unit sphere
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9h
revised Looking for differentiable functions $f$ such that the set of points at which $|f|$ is not differentiable has some particular properties
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10h
revised Showing that Lebesgue measure is preserved by translations of the $d$-dimensional torus
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10h
answered Matrix tranformation, how to
11h
comment Find the locus of points M the difference of the squares of whose distances from two given points A and B is equal to a given value c.
You are on the wrong track. Perform the same calculations as you did in your first approach, but using the disposition suggested in my answer. Then interpret the resulting condition on $P=(x,y)$ in words.
12h
answered Looking for differentiable functions $f$ such that the set of points at which $|f|$ is not differentiable has some particular properties
14h
answered Find the locus of points M the difference of the squares of whose distances from two given points A and B is equal to a given value c.
1d
answered Invent transformation mapping ellipsoid to unit sphere
1d
revised How long is the curve that a creature walks?
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1d
comment List of powers of Natural Numbers
What does "do s[i] += s[i-1]" mean?
1d
answered How long is the curve that a creature walks?
1d
comment Lesser known derivations of well-known formulas and theorems
Here is a version of Fuerstenberg's proof: We are arguing about periodic sets of integers. The set $N_p$ of all integers prime to $p$ is periodic, and the intersection of two periodic sets is periodic. If there were only finitely many primes the set $\{1,-1\}$ would be periodic.
1d
comment An inequality for powers of reals
Apart from a typo your proof now can be finished by noting that $f'(x)<0$, since $x\mapsto x^\alpha$ is decreasing when $\alpha<0$.
2d
comment When an equation has no solutions, denote it with $x\in\varnothing$.
An equation (or a system of equations) in so many variables has a solution set $S$ which is a subset of the universe $\Omega$ for which the equations make sense. When there are no solutions we write $S=\emptyset$. A statement as $(x_1,x_2,\ldots, x_n)\in\emptyset$ seems pretty forlorn to me.
2d
comment Find a 3rd order linear homogeneous differential equation with constant coefficients whose solution is $y=x\sin(x)$
@pooja: See my edit.
2d
revised Find a 3rd order linear homogeneous differential equation with constant coefficients whose solution is $y=x\sin(x)$
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2d
comment Equilateral triangle is cut in $4^n$ congruent equilateral smaller triangles
Replace "you are done" by "tile the four $4^n$-triangles using the induction hypothesis, leaving the top tiny triangle of the $4^{n+1}$-triangle uncovered." I'm not sure whether this "formal" version is really better than the "aha" proof given above.
2d
answered Equilateral triangle is cut in $4^n$ congruent equilateral smaller triangles
2d
answered Find a 3rd order linear homogeneous differential equation with constant coefficients whose solution is $y=x\sin(x)$
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