Law of sines

The purpose of this presentation is to guide students to build, step by step, a triangle to: (1) Check the law of sines in some particular cases and (2) Show that by inscribing the triangle inside a circle, twice the distance (2r) of the center of the circle to any of the triangle is equal to the length of any side of the triangle (a, b or c) divided by the sine of the opposite angle.