Circle annulus

There are 2 concentric circles in the figure. Chord of larger circle 10 cm long is tangent to the smaller circle. What are does annulus have?

Result

S =  78.54 cm2

Solution:

R2=(10/2)2+r2 R2−r2=52 S=π⋅ R2−π⋅ r2 S=π⋅ (R2−r2)  S=π⋅ 52=3.1416⋅ 52≐78.5398≐78.54 cm2R^2=(10/2)^2+r^2 \ \\ R^2-r^2=5^2 \ \\ S=\pi \cdot \ R^2 - \pi \cdot \ r^2 \ \\ S=\pi \cdot \ (R^2-r^2) \ \\ \ \\ S=\pi \cdot \ 5^{ 2 }=3.1416 \cdot \ 5^{ 2 } \doteq 78.5398 \doteq 78.54 \ \text{cm}^2

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