什么是角？

An angle:$\angle$ is a figure made by two $\color{red}{rays}$ that have the same endpoint. The two $\color{red}{rays}$ are called the sides of the angle, and their common endpoint is the vertex of the angle.

An angle's measure is how open it is. We determine an angle's measure by using a protractor.

Consider the protractor above. We see that it represents an angle measurement of $90^\circ$.

Congruent angles are angles that have equal measures; if angles have equal measures they are said to be congruent.

An angle is a figure formed by the intersection of two rays.

Correct! And when two rays share the same head, we say that they form an angle. We call the shared point the vertex of the angle.

We reference the angle by the points that form its rays, and we always reference the vertex angle in the middle. You can think of this as the order in which we draw the points.

You can imagine if we were to draw the angle, we would draw the points in the order $B$, $A$, $C$, so that's how we name the angle.

Okay, what if I told you that you have two intersecting lines?

You're probably thinking "Thanks, now what does this give me? I know they intersect at a point, but why do you want me to consider these darn things?"

What if I now told you that they just created 4 angles? You're now thinking, "What are angles? You said there are 4 of them.

An angle is the space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet. So now, measure the angle between the lines you just got with a protractor.

Two rays with a common end point form an $angle$. The two rays are called the sides or arms of the angle.

The common endpoint is called the $vertex$ of the angle. Angles are measure in $degrees$ or $radians$.

An angle is a figure formed by two intersecting rays.

Intersecting lines form 4 angles.

(Video) Angle Basics

by Math Antics

Here's a video by mathantics explaining the basics of angles.

Angles are the space formed between 2 intersecting lines. When 2 lines intersect, 4 angles are formed. When 3 angles intersect at the same point, 6 angles are formed and so on. Angles are measured in degrees and to find the measure of an angle, you use a protractor.