Circle Theorem: Two Radii Make an Isosceles Triangle

Circle Theorem: Two Radii Make an Isosceles Triangle

Two radii of a circle form the two equal sides of an isosceles triangle.

Note: Radii is the plural of radius.

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.

A circle is a set of points that are all the same distance from the center. The radius is the same wherever in the circle it is drawn.

Two radii will be of equal length.

A triangle can be drawn by joining the ends of the two radii together.

Two sides of this triangle are the radii of the circle and the same lengths.

A triangle with two equal sides is an isosceles triangle.


The slider below shows a real example which uses the circle theorem that two radii make an isosceles triangle.

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See Also

What is a circle? What are the circle theorems? What is an isosceles triangle? What is a triangle? The interior angles of a triangle