(1 x n) + (2 x (n-1)) + (3 x (n-3)) + ... + ((n-1) X 2) + (n x 1) = ?
(1) n(3n + 1)/2
(2) 2n(3n + 1)/3
(3) n(n + 1)(n + 2)/6
(4) n(n-1)(n-2)/2
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(1 x n) + (2 x (n-1)) + (3 x (n- 3)) + ... + ((n-1) X 2) + (n x 1) = ? (1) n(3n + 1)/ 2 (2) 2n(3n + 1)/3 (3) n(n + 1)(n + 2)/6
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