The six trigonometric functions are sine, cosine, tangent, cotangent, secant and cotangent. In mathematical analysis, trigonometric function is also defined as the solution of infinite series or specific differential equation, which allows its value to be extended to any real value or even complex value.

Trigonometric functions are generally used to calculate the sides and angles of triangles with unknown lengths, and are widely used in navigation, engineering and physics. In addition, taking trigonometric functions as templates, we can define a class of similar functions, which are called hyperbolic functions. Common hyperbolic functions are also called hyperbolic sine functions, hyperbolic cosine function and so on. Trigonometric function (also called circular function) is a function of angle; They are very important in studying triangles, simulating periodic phenomena and many other applications.

Definition of trigonometric function of right triangle

In a right triangle, when the connecting lines AB, AC and BC of three points A, B and C on the plane form a right triangle, where ∠ACB is a right angle. For ∠BAC, the opposite side A = BC, the hypotenuse) c=AB, and the adjacent side B = AC.