Some Theorems
Newton binomial theorem
\((a+b)^n=\sum\limits_{i=0}^n{n\choose i}x^iy^{n-i}\)
Basic combinatorics
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Origin www.cnblogs.com/cjoierShiina-Mashiro/p/12120052.html
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\((a+b)^n=\sum\limits_{i=0}^n{n\choose i}x^iy^{n-i}\)