Cosine theorem formula of trigonometric function: f(x)=COsx (xER). Cosine (cosine function), a kind of trigonometric function. In Rt△ABC (right triangle), ZC = 90°, and the cosine of zA is the hypotenuse of its adjacent side than the triangle, that is, cosA=blc, which can also be written as cosa=ACIAB.
Trigonometric function is one of the basic elementary functions, which takes the angle (the most commonly used radian system in mathematics, the same below) as the independent variable, and the angle corresponds to the coordinates where the terminal edge of any angle intersects with the unit circle or its ratio as the dependent variable. It can also be equivalently defined as the lengths of various line segments related to the unit circle. Trigonometric function plays an important role in studying the properties of geometric shapes such as triangles and circles, and is also a basic mathematical tool for studying periodic phenomena.
practical application
In real life, cosine theorem is an intelligent recommendation system in computer technology and one of the basic algorithms in news classification.
From Wu Jun's book The Beauty of Mathematics, we know that cosine formula can be used to classify news and users.
Quote from the article "The Beauty of Mathematics": "A vector is actually a directional line segment in a multidimensional space.
Two vectors are similar if their directions are the same, that is, the included angle is close to zero. To judge whether the directions of two vectors are consistent, it is necessary to calculate the included angle of vectors by cosine theorem. "
"When the cosine of the included angle between two news vectors is equal to 1, the two news are completely duplicated (so that the duplicated pages can be deleted); When the cosine of the included angle is close to 1, the two news stories are similar and can be classified into one category. The smaller the cosine of the angle, the smaller the correlation between the two news. " Similarly, it can be used to calculate the similarity of users or goods in the recommendation system.