71,741 reputation
147135
bio website math.ethz.ch/~blatter
location Switzerland
age 79
visits member for 4 years, 5 months
seen 7 mins ago

Jan
16
answered A Proof that Orthogonal Complement is unique
Jan
16
revised Find all linear maps (all 3x3 matrices) whose img(A) is spanned by <1 1 1>, <-1 0 1> and ker(A) is spanned by <-1 2 0>
added 338 characters in body
Jan
16
answered Find all linear maps (all 3x3 matrices) whose img(A) is spanned by <1 1 1>, <-1 0 1> and ker(A) is spanned by <-1 2 0>
Jan
15
comment Is every hypersurface in $\mathbb{R}^n$ the boundary of an open domain?
A smooth Jordan curve in the plane, parametrized with respect to arc length, is a compact hypersurface in ${\mathbb R}^2$. That it is bounding an open domain is not easy to prove even in the smooth setting.
Jan
15
answered How do you simplify in writing $[1, \infty) \cap [2, \infty) \cap [3, \infty) \ldots $ , in Real Analysis?
Jan
15
revised Finding extrema: When can you replace $f$ by $\phi\circ f$, or vice versa?
edited title
Jan
15
answered Is there a non-ambiguous name for the “square of a function”?
Jan
15
revised Intuitive understanding of the $BAB^{-1}$ formula for changing basis in linear transformations.
added 108 characters in body
Jan
15
answered Intuitive understanding of the $BAB^{-1}$ formula for changing basis in linear transformations.
Jan
15
comment Surface all of whose normals intersect at a point
@orangeskid: After we have proven that $S$ is part of a sphere it is obvious that $\|\gamma(s)-M\|$ is constant along all curves $\gamma\subset S$.
Jan
15
revised Surface all of whose normals intersect at a point
added 21 characters in body
Jan
15
awarded  Revival
Jan
15
comment Surface all of whose normals intersect at a point
@Mariano Suárez-Alvarez: Note that all these circles have the same radius, given by the distance from p to the common point of intersection of the normals.
Jan
14
answered Surface all of whose normals intersect at a point
Jan
14
answered Inverse gradient as line integral in Mathematica
Jan
14
revised Let $w, x, y, z$ be natural numbers. Find the correct alternative.
added 19 characters in body
Jan
14
answered Derivation of fourier series equation
Jan
14
comment Number of one -to-one functions
The OP had "either – or"; so maybe the correct answer is $(120-24)+(125-24)=197$.
Jan
14
answered Let $w, x, y, z$ be natural numbers. Find the correct alternative.
Jan
14
revised $f'(t)\rightarrow b$ as $t\rightarrow +\infty$ $\Rightarrow f (t)/t\rightarrow b $ using Mean Value Theorem
edited body