1
An arc with a long radius.
Among them, radian: understood as a segment of a circle.
The length of a segment of a circle is R.
Then the central angle corresponding to this arc is called the angle of 1 radian.
In this concept, you first understand the concepts of arc and central angle, and then simply understand it.
In order to make it easier to remember, it is best to draw a picture and find the arc and the central angle yourself.
2
Meet the unit leader. You can interpret the unit leader as the number 1.
Unit circle (that is, a circle with a radius of 1
This sentence:
The absolute value of the radian number of the angle α is equal to the arc length of the central angle α.
The arc length of the central angle α is equal to the absolute value of the radian number of the angle α.
In this way,
It is the problem of calculating the arc length of the central angle α with radians.
| radian | * radius R= arc length
Because the radius R= 1
So | radian | * radius R= arc length
The radian here is an absolute value, because the angle is divided into positive and negative points.
I suggest you look at the link below.