Cos is the cosine value, and the cosine value of du = adjacent side ÷ hypotenuse. Because the straight is triangular, the right-angle knife edge facing 30 is half of the hypotenuse. So the ratio of the three sides of this triangle = 1: √ 3: 2.

Extended data:

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.