This depends on how many pages you read all together. I don't fully understand what the question is that you are asking. Could you try to explain it a little bit more? If you can then I could probably help you out :)
The radius is the distance from the center to any point. The distance from (2,1) to (0,1) is of course 2. The general formula for a circle with radius r and center (a,b) is

In our case we get
B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B
Answer:

Step-by-step explanation:
The difference of two cubes formula is given as:

Unsure of what you are asking!
But if the issue here is how to define a line segment, write what you do know and then reconsider "undefined terms."
A line segment is a straight line that connects a given starting point and given ending point.
If you consider a circle of radius 3 units, the radius can be thought of as the line segment connecting the center of the circle to any point on the circumference of the circle.
If the center of a given circle is at C(0,0) and a point on the circumference is given by R(3sqrt(2),3sqrt(2)), then AC is the line segment joining these two points. This line segment has length 3 and is in the first quadrant, with coordinates x=3sqrt(2) and y=3sqrt(2) describing the end point of the segment.