Annulus

The radius of the larger circle is 8cm, the radius of smaller is 5cm. Calculate the contents of the annulus.

Correct result:

S =  122.522 cm2

Solution:

r1=8 cm r2=5 cm  S1=π r12=3.1416 82201.0619 S2=π r22=3.1416 5278.5398 S=S1S2=201.061978.5398=122.522 cm2r_{1}=8 \ \text{cm} \ \\ r_{2}=5 \ \text{cm} \ \\ \ \\ S_{1}=\pi \cdot \ r_{1}^2=3.1416 \cdot \ 8^2 \doteq 201.0619 \ \\ S_{2}=\pi \cdot \ r_{2}^2=3.1416 \cdot \ 5^2 \doteq 78.5398 \ \\ S=S_{1}-S_{2}=201.0619-78.5398=122.522 \ \text{cm}^2



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