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14h
comment Visualize $z+\frac{1}{z} \ge 2$
Not everything else...
14h
comment Visualize $z+\frac{1}{z} \ge 2$
Convexity is a geometric concept...
14h
answered Visualize $z+\frac{1}{z} \ge 2$
1d
awarded  Critic
1d
answered Questions about Eigenspace
1d
comment A complex variable function integrated over an infinitesimal disk
The proof really only uses the fact that $f$ is continuous in the disc...
1d
comment Topological proof that the interval $[a,b)\subset \mathbb{R}$ is not closed
$b$ has no open set around it in your argument...
1d
comment Let $D$ be a nonsingular diagonal matrix. Show that $1\notin spec(DA)$ if and only if $D - A$ is nonsingular.
For $A$ and $D$ to commute...
1d
comment If $f(X+a) = f(X-a)$ where $a$ is infinitesimally small then…
This is a calculus problem, not abstract mathematics...
1d
comment Let $D$ be a nonsingular diagonal matrix. Show that $1\notin spec(DA)$ if and only if $D - A$ is nonsingular.
$D$ may have to be a scalar multiple of identity...
1d
comment If $f(X+a) = f(X-a)$ where $a$ is infinitesimally small then…
Correct, if the graph of $f$ is a curve...
1d
answered Prove family of function is not equicontinuous
1d
revised If $f(X+a) = f(X-a)$ where $a$ is infinitesimally small then…
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1d
answered If $f(X+a) = f(X-a)$ where $a$ is infinitesimally small then…
May
22
comment Is there a name for the relationship between matching combinations?
It's probably too elementary to have a name. It follows from the symmetry of the binomial coefficients and Pascal triangle...
May
21
comment Is there a name for the relationship between matching combinations?
The identity is obvious from taking complements in the "n choose k" combinatorial definition...
May
20
comment How to calculate whether a ray intersects an arbitrarily oriented bounding box?
Find the equations for the planes through the sides of the box (e.g. using the three points). Then find the points of intersections of the ray and the planes (solving systems of three equations) and check if these are on the sides (check inequalities w/the planes equations and the coordinates of the vertices to make sure they're at the same half-spaces of the dividing planes). There's a cool problem of finding trajectoty of a ray reflecting in a box...
May
19
comment How to calculate whether a ray intersects an arbitrarily oriented bounding box?
Is it a rectangular box?
May
19
comment Are there mathematical objects that have been proved to exist but cannot be described in words?
There're mathematical objects that are difficult to visualize...
May
19
comment Does the closed form of $f(t) = \int \frac{e^{2 \pi i \alpha t}}{e^{2 \pi i \beta t} - 1} dt$ exist?
The integrand denominator is a sum of geometric series...