In 1946, ErdÐ â s himself posed a riddle about what are called “isosceles sets”: How many points can you place in d -dimensional space such that any three of them form an isosceles triangle?

An isosceles triangle with one angle greater than 90° is an obtuse-angled triangle. An isosceles triangle with angles of 100°, 40° and 40° is an obtuse-angled triangle.

Working with Sketch 2 Project Sketch 2 on the screen and ask the students to explore which coloured triangles could fit into the given triangle outlines. For this sketch, the eyes and nose outlines ...

Students are often unsure why angles in the same segment of a circle have to be equal. Colin Foster explains how to make it ...

You'll be using Sketch 1 of this file which has three different types of triangles - scalene, isosceles, equilateral. Each triangle type has a different colour (pink for scalene, red for equilateral, ...