Two annuluses

The area of the annular circle formed by two circles with a common center is 100 cm2. The radius of the outer circle is equal to twice the radius of the inner circle. Determine the outside circle radius in centimeters.

Correct result:

r2 =  6.5147 cm

Solution:

S=100 cm2 r2=2 r1 S=S2S1=π r22π r12 S/π=r22(r2/2)2 S/π=r22r22/4 r2=S/π/(11/4)=100/3.1416/(11/4)6.5147 cm   Verifying Solution:  r1=r2/2=6.5147/23.2574 cm S3=π r22π r12=3.1416 6.514723.1416 3.25742=100 S3=S  r2=6.5147=6.5147 cm



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