It will be a few years before we get to celebrate the next Pythagorean Theorem Day in July of 2025. Here are some ideas for celebrating this fun mathematical holiday. For many, the Pythagorean theorem (also known as Pythagoras’ theorem) is one of the most memorable formulas from high school math. Most adults would likely …

# Triangles

I use these classifying triangles by angles and sides notes with my pre-calculus students as part of our first unit of the year which covers mainly geometry review. Especially with the pandemic, I have to spend quite a bit of time reviewing geometry before we can jump properly into trigonometry. I have my students fill …

Sankaku puzzles are a geometric based logic puzzle that focuses on finding the area of a triangle. The goal of each puzzle is to connect three dots to form a triangle with the specified area. Sankaku puzzles are the creation of Naoki Inaba, a prolific Japanese puzzle creator. I first discovered these puzzles several years …

This tricky triangles puzzle has been around for over a century – can you arrange these eight sticks to form exactly four triangles and two squares? The original puzzle was meant to be solved with matchsticks, but I don’t think I need to explain why I won’t be giving my students matchsticks to play with… …

It’s November which means it’s finally time to pull out this Triangular Turkey puzzle for Thanksgiving. How many different triangles can you find in this picture of a Thanksgiving turkey? I ran across this triangular turkey puzzle in a Martin Gardner book (Perplexing Puzzles and Tantalizing Teasers) this summer, and I knew I had to …

I’m excited to get back to featuring a new puzzle of the week every week in my classroom this year. A new puzzle I have prepped for this year is called Three of Five. Three of these five figures fit together to create a triangle. Which ones are they? I ran across this puzzle in …

I created these SOH CAH TOA notes for my Pre-Calculus students a few years ago to review how to find the trigonometric functions of an angle, given a triangle. First, we reviewed the different parts of a right triangle. I have also created a poster of the parts of a right triangle that might be …

Looking for a challenge? Check out this page of Make It Pythagorean Puzzles. Insert the same digit (in any manner of your choosing) to each side of the triangle to form a right triangle. I ran across these interesting puzzles in Golf on the Moon by Dick Hess (Dover Publications).

The Parts of a Whole Puzzle gives students five shapes that must be arranged to form a triangle whose three sides are of equal length. In other words, form an equilateral triangle. I would have renamed this as the Equilateral Triangle Puzzle, but I have already shared a different equilateral triangle puzzle on my blog …

I am really excited about this shape grid puzzle from Erich Friedman. The goal of the puzzle is to divide the grid into geometric shapes. Any lines you draw must follow either the grid lines or the diagonals of the grid squares. Each shape that you draw must contain exactly one shape icon inside. This …