Mark the 90° right angles in the bottom left and top right corners. You can split a rectangle into 2 right-angled triangles.

A simple guide on how to show the angles in triangle add up to 180 degrees, aimed at students aged 11 to 14.

Essay How Many Triangles Are There? Here’s How to Solve the Puzzle Counting will get you nowhere. Try a little combinatorics instead. Share full article 146 ...