And now, delta r should be essentially roughly equal to, well, its direction will be tangent to the trajectory.
这里，△r应该是近似等于。。。,它的方向是轨道的切线方向。
Passenger and cargo transportation flow is in the direction of the Yangtze River Delta region.
客货运输的主要流向是长三角方向。
Passenger and cargo transportation flow is in the direction of the Yangtze River Delta region.
客货运输的主要流向是长三角方向。
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