When you integrate this, - the motion that we try to do — we keep this fixed and then we just rotate around the origin.

算出这个积分，我们要做的是-，把原点固定，然后绕着原点旋转。

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r No matter which direction I go from the origin, r=a if I fixed it,r goes from zero to r equals a.

,无论从原点沿着哪个方向走，只要固定方向，r就是从0开始到。

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So trades, nicknames, places of origin, and fathers' names became fixed surnames - names such as Fletcher and Smith, Redhead and Swift, Green and Pickering, Wilkins and Johnson.

因此，职业、昵称、家乡和父亲的名字就用来当作姓氏——例如，富勒特彻和史密夫，利德·希特和斯福特，格林和皮克灵，威肯斯和约翰逊。

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