In the figure below, the circumference of big circle and small circle are 31.4cm and 25.12cm respectively

In the figure below, the circumference of big circle and small circle are 31.4cm and 25.12cm respectively

Big circle radius: (31.4 / 3.14) / 2 = 5cm
Small circle radius: (25.12 / 3.14) / 2 = 4cm
Annular area: π * 5 * 5 - π * 4 * 4 = 9, π = 28.26 (cm2)
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A math problem. The circumference of a semicircle is 25.7cm. How many square centimeters is its area?
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Let the diameter of semicircle be x cm
πX÷2+X=25.7
3.14X+2X=51.4
5.14X=51.4
X=10
(x △ 2) & sup2; * 3.14 * 0.5 = 39.25 square centimeter