Recurence formula of permutations:
Recurence formula of arrangements:
Recurrence formulas of Combinations:
Formula complementary combinations:
Formula Newton's binomial theorem is:
Termenul general al dezvoltarii binomului lui Newton:
We notice that,
Finding the highest rank within the development (a + b)n is done by formula
Note. For a set with n items the number of subsets with k elements equal Cnk.
For a = b = 1, we get
Note. The number of subsets of set with n items is 2n.
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