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A comment on Generating all permutations, combinations, and power set of a string (2012). Parent comment
Given Set A = {1, 2, 3}
This is the power Set of A P(A) = {{}, {1}, {2}, {3}, {1, 2}, {1, 3}, {2, 3}, {1, 2, 3}} (All the subsets of A including the empty set and A itself)
3 choose 2 = 3 (If you look in the power set, you'll see that there are only 3 ways to choose 2 items out of 3)
Note that order does not matter.
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Given Set A = {1, 2, 3}
This is the power Set of A P(A) = {{}, {1}, {2}, {3}, {1, 2}, {1, 3}, {2, 3}, {1, 2, 3}} (All the subsets of A including the empty set and A itself)
3 choose 2 = 3 (If you look in the power set, you'll see that there are only 3 ways to choose 2 items out of 3)
Note that order does not matter.