This video tutorial [5:35] explains that if the diameter of a circle is one of the sides of a triangle inscribed in the circle then the triangle is a right triangle. This video also appears in the strand Geometry: Circles.

Demonstrates how to find the area of an equilateral triangle inscribed in a circle by applying the area formula for a circle and Heron's formula. Some basic trigonometry (SOHCAHTOA) is also used. [11:38]

This video tutorial explains that if the diameter of a circle is one of the sides of a triangle inscribed in the circle then the triangle is a right triangle.

Students explore a problem that requires then to figure out the area of an equilateral triangle inscribed in a circle using a little trigonometry.