Question

area enclosed by two concentric circles is 770cm²,if the radius of outer circle is 21cm ,then radius of inner circle is​

Answer 1

Answer:

Given: R=21cm

area enclosed by two concentric circles = 770cm²

πr²-πR²=770

π(r²-R²) = 770

22/7 (r²-21²) = 770

r²-441 =770*7/22

r²=490+441

r² = 931

r=30.5

Answer 2

Answer:area enclosed by two concentric circles= area of ring formed both the circles

=> ar=π{R²-r²} [where, R is the radius

of larger circle and r

is that of smallercircle]

770=π(21²-r²)

770/π=441-r²

770×7/22=441-r²

245=441-r²

r²=441-245

r=√196

r= 14

Hence, radius of inner circle is 14 cm.