扇形面积公式 / 推导
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S圆 = πR2
120° = 13 × 360°
S扇 = 13 S圆
= 13 πR2
= 13 πR2
90° = 14 × 360°
S扇 = 14 S圆
= 14 πR2
S扇 = 14 S圆
= 14 πR2
n° = n360 × 360°
S扇 = n360 S圆
= n360 × πR2
S扇 = n360 S圆
= n360 × πR2
= π6
代入 n=60, R=1