GraphicMaths

Visualising maths

Two radii form an isosceles triangle

A triangle formed by two radii of a circle is an isosceles triangle.

2 radii

Interactive example

In this interactive resource, try dragging the red dots around the circumference of the circle:

As you can see the two angles at the circumference are also always equal.

Proof

By definition, any triangle with two equal sides is an isosceles triangle. Any isosceles triangle also has two equal angles.