These two are basic trigonometric functions, which should be encountered in junior middle school, in which sin is a sine function and cos is a cosine function. The specific meaning is as follows:

Sine function sinA: it represents the ratio of the opposite side of ∠A (non-right angle) in a right triangle to the hypotenuse of the triangle;

CosA function: represents the ratio of the adjacent side of ∠A (non-right angle) to the hypotenuse of the triangle in a right triangle;

It is represented in the following figure (where ∠ c = 90):

Of course, sine and cosine functions can be specifically represented by right triangles, but it does not mean that they can only be summarized by right triangles. Any angle with sine and cosine values includes an obtuse angle and an angle greater than 360, that is, the result of a in the above formula can be any real number, including negative numbers and 0.

Supplementary knowledge: tangent function is also often used. A in its formula can also be greater than 360, but it is not all real numbers, because there are several angles that have no tangent value, such as 90. The value that a cannot take should be A ≠ 90+ 180× N, where n is an integer.