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2011-09-20 17:21:00   来源：作文地带整理    双击单词自动翻译

　　Suppose once again that the minute hand of a clock is a vector of magnitude 4 and the hour hand is a vector of magnitude 2. If, at 5 o’clock, one were to take the cross product of the minute handthe hour hand, what would the resultant vector be?

　　First of all, let’s calculate the magnitude of the cross product vector. The angle between the hour hand and the minute hand is 150o:　　Using the right-hand rule, you’ll find that, by curling the fingers of your right hand from 12 o’clock toward 5 o’clock, your thumb points in toward the clock. So the resultant vector has a magnitude of 4 and points into the clock.

（责任编辑：申月月）