theonefreshmen
theonefreshmen
25.03.2020 • 
Mathematics

Slader In this problem we want to calculate the number of two element lists (a, b) we can form using the numbers 0, 1, . . . n with a < b. (a) Show that the answer is (n + 1)n/2 by considering the number of two-element lists (a, b) in which a < b or a > b. (b) Show that the answer is also 1 + 2 + 3 + · · · + n. Taken together (a) and (b) prove the formula Xn k=1 k = (n + 1)n 2

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