Which of the following are known as two circles with equal radii with different centres?
Congruent circles
Equal circles
Concentric circles
Semi-circles
Two or more circles with equal radii, regardless of centre point position are known as Congruent or Equal circles.
The adjacent figure consists of four small semi-circles of equal radii and big semi-circles of equal radii (each 21cm). Find the area of the shaded region.