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1 / 2 + 1 / 2 * 3 + 1 / 3 * 4 + 1 / 4 * 5 + 1 / 5 * 6 + 1 / 6 * 7 + 1 / 7 * 8 + 1 / 8 * 9 + 1 / 9 * 10
1 = 1 - 1/2 1/(2×3) = 1/2 - 1/3 ……………………………… 1 / [n (n + 1)] = 1 / N - 1 / (n + 1) original formula = 1 - 1 / 2 + 1 / 2 - 1 / 3 + 1 / 3 - 1 / 4 + + 1/9 - 1/10 = 1 - 1/10 = 9/10
1 + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10... + 100 =
It's right to add 1 to the answer upstairs
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