Sine theorem: (Sine law) is a basic theorem in trigonometry, which points out that "in any plane triangle, the ratio of sine value of each side to its diagonal is equal and equal to the diameter of the circumscribed circle", that is, a/sinA=b/sinB=c/sinC= 2r=Dr is the radius of the circumscribed circle, and D is the diameter.
Analysis of cosb formula of trigonometric function
Cosa-cosb=-2, this formula belongs to the formula of trigonometric function, and the formula of trigonometric function seems complicated, but as long as we master the essence and internal law of trigonometric function.
You will find that there is a strong connection between the formulas of trigonometric functions. And mastering the inherent law and essence of trigonometric function is also the key to learn trigonometric function well.
Trigonometric function belongs to transcendental function in elementary function in mathematics. Their essence is the mapping between a set of arbitrary angles and a set of ratio variables. Usually, trigonometric functions are defined in a plane rectangular coordinate system.