Using Menelaus’ theorem to show points are collinear
38396
If $AD$, $BE$, $CF$ are exterior bisectors then $D,E,F$ are collinear
157213
Application of Luca's theorem
153767
Singular points and tangent lines
57514
The Minkowski sum of two convex sets is convex
47342
Figure out if a fourth point resides within an angle created by three other points
119978
Equidistant points on a polyline
155004
Maximal points on an $n$-dimensional ellipsoid
14475
When can we speak of collinearity
147429
Set of points in $\mathbb{C}$ s.t. $z^{n-1} = \overline z$
17459
Determining if an arbitrary point lies inside a triangle defined by three points?
94270
Test if point is in convex hull of $n$ points
71074
The locus of the intersection point of two perpendicular tangents to a given ellipse
2357
Showing $\frac{x^3y}{x^4+y^2}$ is continuous at all points
145756
Collinearity problem (Newton-Gauss line)
110472
Existence of a Pivot Point in Euclidean Geometry
88605
Proof of the Reverse Triangle Inequality
20407
Proof of Wolstenholme's theorem