设æå½¢çåå¾ä¸º R ã
âR^2 * 120/360 = 300â
R = 30
æå½¢çåå¼§é¿ L = 2âR * 120/360 = 20â
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设åé¥åºé¢åå¾ä¸º r ã
2âr = 20â
r = 10
æ ¹æ®å¾è¡å®çï¼åé¥çé«Hçå¹³æ¹çäºæ³çº¿å¹³æ¹åå»åºé¢åå¾çå¹³æ¹
H^2 = 30^2 - 10^2
= 800
H = 20â2
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S = 10*2*20â2/2
= 10*20â2
= 200â2
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