brainjam's user avatar
brainjam's user avatar
brainjam's user avatar
brainjam
  • Member for 13 years, 6 months
  • Last seen this week
22 votes
Accepted

Does there exist a circle with EXACTLY two rational points, no more, no less?

7 votes
Accepted

An ellipse inside a heptagon

7 votes
Accepted

Dandelin's proof of Pascal's theorem

6 votes
Accepted

Convexifying a Concave Polygon by Reflections

5 votes
Accepted

On a Geometric Proof (Ahlfors) that the Cross ratio is real if and only if four points lie on a circle or straight line

5 votes
Accepted

Perspective view of longitudinal great circles - ellipses inside a circle

5 votes

Let $A=(-1,0),B=(1,0), C$ be points in $\mathbb{R}^2.$ What is the locus of points $\{s\in\mathbb{R}^2:C$ lies on the angle bisector of $AsB$}?

5 votes
Accepted

$S^3$ as union of 2 solid tori

5 votes

A geometry problem with the reflection of the incenter

5 votes

Why is euclidean geometry also called parabolic geometry?

4 votes
Accepted

Constructing the center of a circle, straightedge only. Variants on the Poncelet-Steiner Theorem

4 votes

Is a symmetric positive definite matrix always diagonally dominant?

4 votes

Strange point lies on common tangent of 9-point circle and incircle

4 votes
Accepted

Showing triangulation of equilateral triangle is non-regular

4 votes

Eight points in a fixed circle

4 votes
Accepted

Geometric proof for why the midpoints of parallel chords of a parabola lie on the same line parallel to the axis

4 votes
Accepted

Chosing points so that $5$ tangents determine a conic

4 votes
Accepted

Demonstration of the impossibility to draw a parallel through a point using only a straightedge.

4 votes
Accepted

If the line at infinity is a secant line of a conic then the conic is a hyperbola?

4 votes

$4$ points in order $A,B,C,D$ lie on a circle with the extension of $AB$ meeting the extension of $DC$ at $E$ and that of $AD$ and $BC$ at $F$.

4 votes
Accepted

What geometrical construction can be done with help of conics which aren't possible with compasses and rulers?

4 votes

Inscribed Circles in a Quadrilateral

4 votes
Accepted

Collinearity in bicentric pentagon

4 votes
Accepted

Nice geometric configuration

4 votes
Accepted

How to identify all the right circular cones passing through six arbitrary points

4 votes
Accepted

Given two conics touching each other in two different points, prove the following collinearity

4 votes
Accepted

Is a point at infinity unique?

3 votes
Accepted

For cyclic quadrangle, prove that a line joining orthocenters is concurrent with sides

3 votes
Accepted

Construct a pole to a given line for a conic in a simple way

3 votes

What is a negative inversion?

1
2 3 4 5
7