Question

area of shaded circular ring is 770 centimetres squared and difference between the radii of the two circle is 7 cm find the area of unshaded region.

Answer 1

area of shaded region= π(r1^2-r2^2) = 770

π (r1+r2)*(r1-r2)= 770
22/7*7*(r1+r+2)=770
r1+r2 = 770/22
r1+ r2 = 35
r1 = 35-r2
r1-r2= 7
r1 = 7+ r2
35-r2 = 7+ r2
35+7=r2+r2
42 = 2*r2
r2= 21
area of unshaded region = π r2^2
= 22/7*21*21
= 22*3*21
= 1386 cm ^2.