Prof. Sally Keely

Attn Calc II students: Saw this integral on Stack Exchange today: \( \int_{0}^{2\pi}\sin(x)\sin(2x)\sin(3x)\sin(4x)\ dx=\frac{\pi}{4} \) Wolfram Alpha confirms So can it be generalized? Yes! Find integral over [0,2pi] of the product of sin(kx), k=1 to n. Discuss in class! (Or over dinner ;-)

2 days ago
Prof. Sally Keely

"Bogs and other peatlands occupy around 3% of Earth’s land. Yet they manage to pack away twice as much carbon as all the planet’s trees. If that carbon were released, atmospheric carbon dioxide would double, with potentially disastrous consequences for humans and many other species."

Mathematicians took on the task of modeling the size/shape of bogs to get good estimates of the potential dangers.

"The bog’s shape seemed to be essentially governed by the physics of the water table. The researchers found that they could mathematically model the shape of the bog by solving a widely used equation named for the 19th-century mathematician Siméon-Denis Poisson that allowed them to approximate a bog’s depth given only the shape of its boundary."

June 02, 2024
Prof. Sally Keely

Attn College Algebra students. ln(x) can be approximated by 2(x-1)/(x+1) and log(x) can be approximated by (x-1)/(x+1). (Try some x-values!) And yet ln(x) is not twice log(x). What's going on here? John D. Cook has useful information about the approximation error here. Watch the scale on the graphs provided. Image source: John D. Cook

May 18, 2024
Prof. Sally Keely

RIP Jim Simons. Mathematician, Billionaire, Philanthropist. He will be missed.

Here Jim provides a short story of his life in mathematics at Abel Prize week in 2022. "I made a lot of money and gave it all away." "I was lucky enough to solve the problem through ambient dimension 7, but in dimension 8 my proof didn't work." So weird, but a common difficulty!

May 12, 2024
Prof. Sally Keely

This is a month late but still worthy math fun. Stolen from MAA's fantastic Math Horizon magazine merely for educational purposes :)

May 11, 2024
Prof. Sally Keely

Happy anniversary of birth to Carl Friedrich Gauss, one of the most prolific mathematicians of all time (b. April 30, 1777).

A fun fact about Gauss is that he figured out a way to draw a 17-sided polygon using only a ruler and compass. "The proof rested on a profound analysis of the factorization of polynomial equations and opened the door to later ideas of Galois theory." (source: image source:

April 30, 2024
Prof. Sally Keely

Attn Calc II students: This is a fun little integral. \( \int 2^{\ln(x)}dx \) A substitition \( u=\ln(x) \) won't work since there is no \( \frac{1}{x} \) to make the match.

Think about before reading on.

Nifty trick! Since \( 2=e^{\ln(2)} \), then \( 2^{\ln(x)} = (e^{\ln(2)})^{\ln(x)}=(e^{\ln(x)})^{\ln(2)}=x^{\ln(2)} \)

Now the integral becomes \( \int x^{\ln(2)}dx = \frac{1}{1+ln(2)} x^{1+\ln(2)} + C \)

Swapping from an constant-to-variable to a variable-to-constant made a world of difference. Sweet!

April 27, 2024
Prof. Sally Keely

Do you use your iPhone Calculator app for quick calculations? In case you didn't know, rotate your phone to landscape and it becomes a scientific calculator with radicals, exponentials, logarithms, trig functions, even hyperbolic trig functions.

Press "2nd" to get more functions including log-base-b, inverse trigs, inverse hyperbolic trigs.

One more hack: Entering numbers into the command line and mess up? No need to "C" clear all, just swipe right on the command line to delete the previous digit.

While DESMOS app and GeoGebra Apps are amazing for graphing, the built-in Calculator app on iPhone is handy! I keep it in my Control Center for easy access.

April 18, 2024
Prof. Sally Keely

Quick read on the history of the decimal point from Scientific American mag.

"The decimal point was a step forward for humanity, enabling the ease and efficiency of calculations that underpin modern science and technology."

April 11, 2024
Prof. Sally Keely
April 08, 2024
Prof. Sally Keely

Solve x/(y+z)+y/(x+z)+z/(x+y)=4 where x, y, z are positive whole numbers. This problem going around the web (blog.computationalcomplexity.o) interestingly IS able to be solved by Perplexity AI, but Genesis AI and ChatGPT each conclude "no solution".

SPOILER! Solution from Perplexity AI:

The equation x/(y+z) + y/(x+z) + z/(x+y) = 4, where x, y, z are positive integers, is a challenging Diophantine equation that has puzzled mathematicians for a long time. The smallest known solution to this equation is:
x = 36875131794129999827197811565225474825492979968971970996283137471637224634055579
y = 36875131794129999827197811565225474825492979968971970996283137471637224634055579
z = -36875131794129999827197811565225474825492979968971970996283137471637224634055579
This solution was found by the mathematicians Andrew Bremner and Allan MacLeod, and published in their 2014 paper "An unusual cubic representation problem".

April 04, 2024
Prof. Sally Keely

Fun and informative spring break sci-fi watch on Netflix: "The Three-Body Problem".

Background info on the and movie review:

Jin (Jess Hong) explains the Three-Body Problem:

March 30, 2024
Prof. Sally Keely

Happy St. Paddy's Day!

"On October 16, 1843, the great Irish mathematician William Rowan Hamilton was walking along the Royal Canal in Dublin. He had been pondering for a long time whether complex numbers could be extended to higher dimensions. During his perambulation, he realized the answer was “yes”, and carved his solution on the Brougham Bridge. The plaque shown [below] commemorates the discovery."

March 17, 2024
Prof. Sally Keely

The title is a bit hyperbolic (pun intended) but I suspect there is at least one item of interest to you.

Happy π Day!

March 14, 2024
Prof. Sally Keely

I've played since 1984 on a black-and-white "portable" Tele-DOS computer (whose "hard" drive was on a 5.25" floppy disk, no kidding). Good article noting the real-world usefulness of transformational and optimization in architecture, engineering, animation, graphic designing, calculus, differential geometry, business, and more. "All of these advanced topics use the same concepts as the simple moves of Tetris."

March 05, 2024
Prof. Sally Keely

Another good read from @johndcook. Unfortunately I can't (won't) boost the toot because the image is missing ALT text.

This-Way-Up and Knuth's Up Arrow Notation:

Love playing with anything Donald Knuth ( The "up arrow" is a repeated exponentiation operator. One of the things that intrigued me early in my study of .

February 15, 2024
Prof. Sally Keely

Attn my II students studying integrals of arctrig functions this week: Fun integration problem whose answer involves both pi and the golden ratio, phi!

\[\int_0^{\pi}\arctan\left(1+\cos x\right)dx=arc\cot\left(\sqrt{\phi}\right)\]

February 09, 2024
Prof. Sally Keely

"Combining mathematics and art is an inevitable extension of their relationship." Art can help one visualize mathematics in a way where new patterns and relationships can be realized. This article shares some specific examples.

February 09, 2024
Prof. Sally Keely

@johndcook posted fun triangle problem yesterday appropriate for a pre-calculus course. I won't "boost" because the sketch is missing . Here is a re-toot instead w/ ALT.

Is this triangle a right triangle? How can you tell? If it is not, what's the measure of the largest angle?

SPOILER! It is not a right triangle (check Pythagorean Theorem). The largest angle measures approximately 90.000003 degrees (by Law of Cosines). Oh so close!

January 30, 2024
Prof. Sally Keely

Beyond the gorgeous photography of ice sheets, glacier covered mountains, blue seas, we get modeling ice sheet mathematics with equations involving partial derivatives explained in intuitive manner. Turn on CC because the audio is really low.

January 19, 2024