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141123
bio website math.ethz.ch/~blatter
location Switzerland
age 79
visits member for 4 years, 1 month
seen 10 hours ago

Sep
20
answered Is it true that $Arg (\prod _{n=1 } ^N p _n )= \sum _{n=1 } ^N Arg (p _n )$?
Sep
20
answered Shortest and most elementary proof that the product of an $n$-column and an $n$-row has determinant $0$
Sep
20
answered The principal curvatures of a surface of revolution
Sep
20
awarded  optimization
Sep
19
answered Giving two equal line segments AC and BD so that they bisect each other at E. Prove that quadrilateral ABCD is a Rectangle.
Sep
19
comment Shortest and most elementary proof that the product of an $n$-column and an $n$-row has determinant $0$
A good answer to this question highly depends on the used definition of determinant, on the set of "known properties" , on allowed operations leaving the determinant unchanged, etc.
Sep
19
answered How to solve this coupled linear differential equations?
Sep
19
answered Using a multivariate chain rule to solve a partial differential equation
Sep
19
revised How do you read the symbol “$\in$”?
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Sep
19
comment High school math definition of a variable: the first step from the concrete into the abstract…
@Ice Boy: The two answers are supplementing each other. See also here: math.stackexchange.com/questions/24284/…
Sep
19
answered Framing a travelling salesman problem
Sep
19
comment How to determine if a triangle can be drawn with the given points.
Have you ever tried to draw a triangle, given three points in the plane?
Sep
19
answered Prove that every set of n points in R3 with diameter L can be covered by a cube with side length L.
Sep
19
revised Five red cards numbered $1,2,3,4,5$ and two black cards both numbered $5$
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Sep
19
revised $T(C)=C$ for some circle C passing through $ z_{0}$. Prove that $T'(z_{0})$ is real.
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Sep
18
answered $T(C)=C$ for some circle C passing through $ z_{0}$. Prove that $T'(z_{0})$ is real.
Sep
18
revised An entire function $f$ that maps horizontal lines to horizontal lines
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Sep
18
answered An entire function $f$ that maps horizontal lines to horizontal lines
Sep
18
answered Five red cards numbered $1,2,3,4,5$ and two black cards both numbered $5$
Sep
18
revised Five red cards numbered $1,2,3,4,5$ and two black cards both numbered $5$
added 9 characters in body