Pythagorean "Paradox" (right-angled triangle).
2786
The staircase paradox, or why $\pi\ne4$
135120
Oppenheim's Inequality for triangles, American Mathematical Monthly problems
42852
The legs of a right triangle with given hypotenuse and radius of inscribed circle
81975
Sequence of triangles with exponentiated sides
33484
The Achilles Paradox
88605
Proof of the Reverse Triangle Inequality
111626
probability of three random points inside a circle forming a right angle triangle
30625
Does the square or the circle have the greater perimeter? A surprisingly hard problem for high schoolers
91258
Drawing a Right Triangle With Legs Not Parallel to x/y Axes?
130436
bisectors of an angle in a triangle intersect at a single point - proof verification
115391
A paradox of length contraction
120196
An angle inside a regular pentagon
120912
Can two Pythagorean triples have the same product?
69077
When the trig functions moved from the right triangle to the unit circle?
65659
Partial derivative paradox
92916
Show that $(2,0,4) , (4,1,-1) , (6,7,7)$ form a right triangle
46989
Degree of freedom paradox for a rigid body