1-(5/7)=((())/(())), think of it this way, think of 1 as ((())/(())), use ((())/(()) ) minus (5/7) to get how many ((())/(())), is ((())/(())).
1-(5/7)=((())/(()))，这样想，把1看成((())/(()))，用((())/(()))减去(5/7)得到多少个((())/(()))，是((())/(()))．
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