Cosine value of angle between straight lines.

The cosine of the angle between a straight line and a straight line is cosα=A? B/(|A|#|B|).

Introduction to cosine function:

Cosine (cosine function), a kind of trigonometric function. In Rt△ABC (right triangle), ∠ C = 90, and ∠A's cosine is the hypotenuse of its adjacent side than the triangle, that is, cosA=b/c, which can also be written as cosa=AC/AB. Cosine function: f(x)=cosx(x∈R).

Corner edge identification method:

1, when a> when bsinA:

When b>a and cosA & gt0° (that is, A is an acute angle), there are two solutions; When b> When a and cosA≤0 are ≤ 0 (that is, A is a right angle or an obtuse angle), there is a zero solution (that is, no solution); When b=a and COSA >; 0 (that is, a is an acute angle), there is a solution; When b=a and cosA≤0 (that is, A is a right angle or an obtuse angle), there is a zero solution (that is, no solution);

2. When a=bsinA:

When cosA & gt0° (that is, A is an acute angle), there is a solution; When cosA≤0 (that is, A is a right angle or an obtuse angle), there is a zero solution (that is, no solution).

Function introduction:

Function, a mathematical term. Its definition is usually divided into traditional definition and modern definition. The essence of these two functional definitions is the same, but the starting point of narrative concept is different. The traditional definition is from the perspective of movement change, and the modern definition is from the perspective of set and mapping.

The modern definition of a function is to give a number set A, assume that the element in it is X, apply the corresponding rule F to the element X in A, and record it as f(x) to get another number set B, assume that the element in B is Y, and the equivalent relationship between Y and X can be expressed as y=f(x). The concept of a function includes three elements: the domain A, the domain B and the corresponding rule F, among which the core is the corresponding rule F, which is the essential feature of the function relationship.

Function was originally translated by Li, a mathematician of Qing Dynasty in China, in his book Algebra. He translated this way because "whoever believes in this variable is the function of that variable", that is, the function means that one quantity changes with another quantity, or that one quantity contains another quantity.