Question

What's is the radius?​

Answer 1

Explanation:

So you have a circle right. The circle is going to have a center point. The diameter of the circle is the length from a side of the circle to the other side that passes through this center point. The radius is half of the diameter. This means that its basically a line starting at the center point and reaches to one side of the circle. In the picture, the diameter is the red line. The radius is half of that red line.

Answer 2

In classical geometry, a radius of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length.