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通过换元可以使看上去很难求解的问题顺利求解,关键在于灵活运用所学知识,采用灵活多变的解题方法,从而使问题顺利获解.
The key problem is to get rid of the seemingly difficult problem by changing hands. The key lies in using the knowledge flexibly and adopting the flexible and resolving method so that the problem can be solved smoothly.