oob73zj92b的部落格

標題:

F.2數學(circles and sectors)

發問:

1. The radii of the front wheel and the rear wheel of a bicycle are 22.5 cm and 18 cm respectively, If the rear wheel makes 50 revolutions, how many revolutions does the front wheel make?2.A ring of radius 10 cm is made of a thin wire. If the ring is cut and the wire is used to make a sector OAB of radius r cm... 顯示更多 1. The radii of the front wheel and the rear wheel of a bicycle are 22.5 cm and 18 cm respectively, If the rear wheel makes 50 revolutions, how many revolutions does the front wheel make? 2.A ring of radius 10 cm is made of a thin wire. If the ring is cut and the wire is used to make a sector OAB of radius r cm with angle AOB=60, find (a) r, (b) the length of arc AB.

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最佳解答:

1. Let n be the number of revolutions the front wheel make the distance of the front wheel and rear wheel ran is the same, so 2(3.14)(18)(50) = 2(3.14)(22.5)n n=40 2. arc AB = 2(3.14)r(60/360) the circumfrence of the ring = the circumfrence of the sector 2(3.14)(10) = 2r + arc AB 62.8 = 2r + 2(3.14)r(60/360) r = 20.6cm arc AB = 2(3.14)(20.6)(60/360) =21.56cm 2007-12-30 16:04:56 補充： 更正:the circumfrence of the ring = the perimeter of the sector

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