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6h
revised Solving $\sec(3\alpha+30^\circ)=\csc(7\alpha-40^\circ)$
added 24 characters in body; edited title
18h
reviewed Reject triangle construction given side, angle and median
22h
answered Show if $A^TA = I$ and $\det A = 1$ , then $A$ is a rotational matrix
1d
comment Interesting cube subdivisions: what is going on here, and what are these polytopes?
On George Hart's "Conway Notation for Polyhedra" page, your construction corresponds to the "ambo" operation. Thus, in Conway notation, your polyhedra are "C" (cube), "aC", "aaC", "aaaC", etc.
1d
revised Prove that $16\cos^5A-20\cos^3A+5\cos A=\cos5A$
Better title
2d
revised Perimeter of a teardrop (made by two adjacent circles)
added 36 characters in body
2d
revised Using trig identities to evaluate $\int_{0}^{\pi/2} \sqrt{1-\sin x} \, dx$
added 11 characters in body; edited title
2d
revised Seeking non-inductive, combinatorial proof of the identity $1^2 + 2^2 + 3^2 + \cdots + n^2 = \frac{n(n + 1)(2n + 1)}{6}$
added 5 characters in body; edited title
Jan
31
comment Which of the $43,380$ possible nets for a dodecahedron is the narrowest?
Just replace your area calculation with a ratio. :)
Jan
31
comment Which of the $43,380$ possible nets for a dodecahedron is the narrowest?
Oh, sure ... That's great for a rectangle that's narrow top-to-bottom. But what if we want a rectangle that's narrow left-to-right? :) (joke)
Jan
30
answered Prove $|x|^2$ = $x^2$
Jan
27
comment why value of Trigonometric ratios of angle and its reference angle are same?
Related: "When the trig functions moved from the right triangle to the unit circle?". In particular, my answer.
Jan
27
comment How far can the plane be tiled by congruent regular pentagons?
Some info on tilings with pentagons: "The trouble with five"
Jan
27
comment How Many Circles go Through 3 Distinct Points of $\mathbb{R}^2 $
Related: "General Formula for Equidistant Locus of Three Points" (from just a few hours ago)
Jan
25
comment How to prove $\sin3θ=3\sinθ-4\sin^3θ$
Related: "Picture/intuitive proof of $\cos(3\theta)=4\cos3(\theta)−3\cos(\theta)$?" My diagram there also shows the sine formula.
Jan
25
awarded  Nice Answer
Jan
23
awarded  geometry
Jan
23
awarded  Necromancer
Jan
20
comment Smallest Circumcircle of Three Triangles
This seems to be the "local" minimum, given this particular configuration of triangles. How do we know that we can't do better "globally" by not requiring two triangles to share an edge?
Jan
19
revised Equalities and inequalities for quadrilaterals in hyperbolic space
edited body