余弦

例句：

1. 1.The angle between two sides of a triangle is the cosine of that angle.
   三角形两边之间的角是该角的余弦。
2. 2.The sine and cosine of an angle are the ratios of the lengths of its sides to the length of its hypotenuse.
   角度的正弦和余弦是其边长与斜边的比值。
3. 3. In trigonometry, the cosine function is used to find the length of a side in a right-angled triangle.
   在三角学中，余弦函数用于计算直角三角形的边长。