The Lesson
Two radii of a circle form the two equal sides of an isosceles triangle.
Why Do Two Radii Make an Isosceles Triangle?
A radius is the line segment from the center of the circle to any point on the circle. The length of this line is also called the radius.



What Is a Circle?
A circle is a shape containing a set of points that are all the same distance from a given point, its center.What Is an Isosceles Triangle?
An isosceles triangle is a triangle with two equal sides and two equal angles across from them.
Interior Angles of an Isosceles Triangle
Two of the interior angles of an isosceles triangle are equal. There are two different angles in an isosceles triangle: the base angle and the vertex angle.
Vertex angle = 180° − 2 × Base angle
Base angle = (180° − Vertex angle) ÷ 2