“就在那个方向上。”他朝北歪了歪头。
不久,他发现自己到了翠林庄,这是他在那个方向上所去过的离家最远的地方。
By-and-by he found himself at Temple Bar, the farthest from home he had ever travelled in that direction.
这个速度要么,在这个方向,要么在那个方向。
The velocity could either be in this direction or it could be in that direction.
The tangent's pointing towards the direction you are headed at that instant.
切线的方向就是,速度矢量在那个瞬时的指向
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