The product of first n positive integer, can be called as n factorial, and noted as n!
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Note, the special case defined,
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When we pick r objects from n objects, if the order matters, it is called as permutation, and we notate it as nPr.
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If the order is unimportant, we can use combination, which is nCr.
+The extra r! is the permutation in the specific set drawn out.
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Note,
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There will be n+1 th term.
+The sum of power of x and y will equal to n.
+The r+1 th term can be called as the general term, in the descending power of x.
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The coefficients, r=0, 1 … are called binomial coefficients.