A visual proof that sin x/x is monotonically increasing on (0, pi/2). For tan x/x, see p. 420 (EJ1017686).

A visual proof that tan x/x is monotonically increasing on (0, pi/2). For sin x/x, see p. 408 (EJ1017684).

In this short article, we prove an identity from which a theorem of Katsuura and two conjectures previously posed in this JOURNAL follow directly.

We discuss the motivation for dimension reduction in the context of the modern data revolution and introduce a key result in this field, the Johnson-Lindenstrauss flattening lemma. Then we leap into high-dimensional space for a glimpse of the phenomenon called concentration of measure, and use it to sketch a proof of the lemma. We end by tying…

An "n"-dimensional generalization of the standard cross product leads to an "n"-dimensional generalization of the Pythagorean theorem.

If students are presented the standard proof of irrationality of [square root]2, can they generalize it to a proof of the irrationality of "[square root]p", "p" a prime if, instead of considering divisibility by "p", they cling to the notions of even and odd used in the standard proof?

Without using limits, we prove that the integral of x[superscript n] from 0 to L is L[superscript n +1]/(n + 1) by exploiting the symmetry of an n-dimensional cube.

Using the fact that the sum of the first n odd numbers is n[superscript 2], we show visually that n[superscript 2] is the same as 0 (mod 3) when n is the same as 0 (mod 3), and n[superscript 2] is the same as 1 (mod 3) when n is the same as plus or minus 1 (mod 3).

What is the area of the (inner) square obtained by slicing the corners off a larger square? This visual proof avoids algebra by considering the area of a parallelogram.

This paper introduces a new matrix tool for the sowing game Tchoukaillon, which establishes a relationship between board vectors and move vectors that does not depend on actually playing the game. This allows for simpler proofs than currently appear in the literature for two key theorems, as well as a new method for constructing move vectors.We…

In this capsule we give an elementary proof of the principal axis theorem within the real field, i.e., without using complex numbers.

A visual proof that the sine is subadditive on [0, pi].

This paper gives a very elementary, essentially visual proof of Viete's product. We employ only the Pythagorean theorem, similarity of triangles, and exhaustion.

Alternating series have the simplest of sign patterns. What about series with more complicated patterns? By inspecting the alternating series test closely, we find a theorem that applies to more complicated sign patterns, and beyond.

If a series of real numbers converges absolutely, then it converges. The usual proof requires completeness in the form of the Cauchy criterion. Failing completeness, the result is false. We provide examples of rational series that illustrate this point. The Cantor set appears in connection with one of the examples.