Find the formula of general term: 4 / 8, 5 / 11, 6 / 14, 7 / 17 There are also 1 / 2, 4 / 3, 6 / 5, 8 / 7

The general formula of 3 / 5, 4 / 8, 5 / 11, 6 / 14 and 7 / 17 is: an = (n + 2) / (3N + 2),
The general formula of 1 / 2, 3 / 4, 5 / 6 and 7 / 8 is: an = 1-1 / 2n, and the value range of n is a positive integer

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9. A formula for calculating compound interest For example, suppose that the principal is 10000 and the monthly income is 10%. Add up the monthly income. That is to say, the principal in the second month is 11000. What is the total income after one year? What is the formula?
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18. Ask: there is a mathematical symbol *, so that the following formula holds: 2 * 4 = 8,5 * 3 = 13,3 * 5 = 11,9 * 7 = 25, then 7 * 3 =?
19. There is a mathematical operation symbol "0", which makes the following formula true: 12023 = 36, 45079 = 1145, 56017 = 642. Find the value of 311045
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