In our daily life, we often use triangles. Why? Because triangles are stable, we can see triangles everywhere in our lives. ?

For example, the roofs of some huts; There are countless supports such as high-voltage telephone poles. Trigonometry played a unique role in ancient times. The early trigonometry was not an independent discipline, but attached to astronomy, which was a method to calculate astronomical observation results. Therefore, the earliest development of trigonometry is spherical mathematics, Greek mathematics, Indian mathematics and Arabic mathematics, but most of them are by-products of astronomical observation. For example, Menelaus in ancient Greece wrote "The Science of the Ball" and put forward the basic problems and concepts of trigonometry, especially Menelaus theorem of the ball science. ?