In ancient times, seeding and harvest time were determined according to the movement of the stars. For this reason, it was of the utmost importance that people studied the sky. These studies led to the discovery of the Trigonometric Ratio; a key to understanding right triangles.

Originally released by PBS, 2012. Streaming video file encoded with permission for digital streaming by Infobase on February 13, 2017.

Mathematica—The Trigonometric Ratio: The Key to Drawing the Skies (8:54); .