Circular shapes - They are those planner shapes that represent the locus of all the points that has a constant distance from a fixed point on the plane. This constant distance is termed as the radius of the circle and the fixed point is known as the center of the circle.
The center of the circle is enclosed by all the points on its periphery.
The circumference of the circle is the total length of its periphery around the center.
Concentric circles are two circles that have the same center
This is a relatively easy half life calculation. After one half-life period, half of the isotope remains. After two half-life periods, one quarter of the isotope remains. That being the case, we see this will take 2 half-life periods or 6 days.
