Cosine formula of the angle between two vectors: cos=ab/a*b, cosine is a kind of trigonometric function. In Rt^ABC (right triangle), < C=90, the cosine of<a is that its adjacent side is the hypotenuse of the triangle, that is, cosA=b/c, which can also be written as cosa=AC/AB. Cosine function: f(x)=cosx(xER). The square of either side of a triangle is equal to twice the product of the sum of the squares of the other two sides minus the cosine of the angle between these two sides and them.

Knowledge expansion

Learning mathematics is a task that requires patience and perseverance. Here are some ways to help you learn math effectively:

Understand the basics: Mathematics is an accumulative subject, so we must first make sure that we have a full understanding of the basic concepts. If necessary, you can review some basic knowledge and establish a solid mathematical foundation.

Grasp mathematical thinking: Mathematical thinking is the key to solving mathematical problems. Cultivating logical thinking, abstract thinking and reasoning ability can be exercised by doing and solving problems.

Make a study plan: make a reasonable study plan and study as planned. Courses and study time can be arranged according to personal learning situation and goals, so as to ensure a certain amount of study time every day.

Actively participate in classroom learning: actively ask questions and participate in discussions in class, interact with teachers and classmates, and better understand and master knowledge.

Do more exercises: Mathematics is a highly practical subject, and doing more exercises is an effective way to consolidate knowledge and improve skills. Choose exercises that suit your level, from simple to complex, step by step.

Ask for help: If you are in trouble or don't understand something, it is very important to ask for help. You can ask teachers, classmates or the math world, and you can also find relevant reference books and online resources.

Attach importance to mathematical practice: applying mathematics to practical problems is an important way to consolidate and improve mathematical skills. Try to solve practical problems, such as applying mathematics to daily life or other disciplines.

In a word, learning mathematics requires persistent efforts and hard training. Through reasonable study methods and unremitting efforts, I believe you will get good grades in mathematics.