The area enclosed between two concentric circles is 770cm2. If the radius of the outer circle
is 21cm, find the radius of the inner circle.
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Answer:
r=14cm
Step-by-step explanation:
Let the radius of the inner circle be r cm. Then,
( π×21×21)−πr
2
=770
π ( 4 4 1−r
2
)=770
7
22
×(441−r
2
)=770
r
2
=196
r=14 cm
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