1. Known: radius of circle r = 2cm, calculate area of circle 2. Known: diameter of circle d = 6cm, calculate area of circle 3. Known: the circumference of the circle is 6.28cm, find the area of the circle 4. It is known that the arc length of 30 ° center angle is 1.57cm, and the area of the arc is calculated The radius of the big turntable in the amusement park is about 50 meters. How many square meters is the area of the circular surface produced by its rotation? How long is the route for tourists to take this big turntable to rotate for a week? The first question is to ask () and the second question is to ask ()

(1) R ^ 2 * π = 12.52 (2) (D / 2) ^ 2 * π = 28.26 (3) l = 2R * π = 6.28, r = 1 area of circle s = R ^ 2 * π = 3.14 (4) 2R * π * 30 / 360 = 1.57, r = 3 area of circle s = R ^ 2 * π = 28.26 (5) area of circular surface generated by rotation s = 7850 length of a circle = 314

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