The sine and cosine of an acute angle are defined in the context of a right triangle: for the specified angle, its sine is the ratio of the length of the side opposite that angle to the length of the longest side of the triangle (the hypotenuse), and the cosine is the ratio of the length of the adjacent leg to that of the hypotenuse.

余弦（cosine）是三角函数的一种。 它的 定义域 是整个 实数集 ，值域是 [ − 1 , 1 ] {\displaystyle [-1,1]} 。 它是 周期函数 ，其最小正周期为 2 π {\displaystyle 2\pi } （360°）。

2025年2月4日 · Definition: Cosine is the ratio of the adjacent side to the hypotenuse in a right triangle, or the x-coordinate of a point on the unit circle. Range: The values of cosine lie between –1 and 1. Periodicity: Cosine is a periodic function with a period of 360° (or 2π radians), meaning it repeats every full circle.

用 弧度制 来表示角的大小，那么任意角的余弦即为一个定义域为，值域为的函数。 该函数是偶函数，具有最小正周期。 函数图像关于直线轴对称，关于点中心对称。 函数在区间上单调递增，在区间上单调递减。 [2] 其中为虚数单位。 余弦函数在复平面解析，其导数为： [3] 对于向量，其与三个坐标轴的正向分别有一个夹角，被称为“方向角”，不妨分别记为。 那么分别称为向量的方向余弦。 方向余弦组成的向量是原向量的单位向量，即满足关系。 此外，三个方向余弦的平方和 …

We can then find the horizontal distance, x, using the cosine function: x = 14 × cos⁡ (25°) ≈ 12.69. The horizontal distance between the person and the plane is about 12.69 miles. Trigonometric functions can also be defined as coordinate values on a unit circle. A unit circle is a circle of radius 1 centered at the origin.

Sine, Cosine and Tangent (often shortened to sin, cos and tan) are each a ratio of sides of a right angled triangle: To calculate them: Divide the length of one side by another side. Example: What is the sine of 35°? Using this triangle (lengths are only to one decimal place): = …

The cosine function cosx is one of the basic functions encountered in trigonometry (the others being the cosecant, cotangent, secant, sine, and tangent). Let theta be an angle measured counterclockwise from the x-axis along the arc of the unit circle. Then costheta is the horizontal coordinate of the arc endpoint.

正弦 （sine）, 余弦 （cosine） 和 正切 （tangent） （英语符号简写为 sin, cos 和 tan) 是 直角三角形 边长的比： 计算方法： 用一条边的长度除以另一条边的长度. 例子： 35°的正弦是多少？ = 0.57... = 0.82…… = 0.70…… 好的计算器都会有 sin, cos 和 tan 的键，方便计算。 你只需输入角度然后按键。 可是你还是要记得它们的意思！ 用图来显示： Well Done! 怎样去记住？ 想想，用这个怪怪的英文单词 "Sohcahtoa"！ Soh... ...cah... 去这页 sohcahtoa 了解更多。 记住它，考试时 …

The cosine function (or cos function) in a triangle is the ratio of the adjacent side to that of the hypotenuse. The cosine function is one of the three main primary trigonometric functions and it is itself the complement of sine(co+sine).

该反余弦x的定义为x的反余弦函数时-1≤x≤1。 当y的余弦等于x时： cos y = x. 然后x的反余弦等于x的反余弦函数，它等于y： arccos x = cos -1 x = y. 例. arccos 1 = cos -1 1 = 0 rad = 0° 请参阅：Arccos函数. 余弦表