Common trigonometric functions are sine function, cosine function and tangent function. In navigation, surveying, engineering and other disciplines, such as cotangent function and secant function will also be used.
Other trigonometric functions, such as cotangent function, dyadic function, cofactor function, semidyadic function, semifactorial function, etc. The relationship between different trigonometric functions can be obtained by geometric intuition or calculation, which is called trigonometric identity.
For greater than? 2π? Or less than or equal to 2π? Angle, you can continue to rotate directly around the unit circle. So sine and cosine become periodic? Periodic function of 2π: For any angle θ and any integer k.
The minimum positive period of a periodic function is called the "basic period" of the function. The basic period of sine, cosine, secant or cotangent is a complete circle, that is, 2π radians or 360; The basic period of tangent or cotangent is a semicircle, which is π radian or 180. Only sine and cosine are directly defined by the unit circle.