1 / 3 + 1 / 5 + 1 / 5 + 1 / 7 + 1 / 7 + 1 / 9 + 1 / 9 + 1 / 11 + 1 / 13 + 1 / 13 + 1 / 15 + 1 / 17 1 ／ 3 + 1 / 3 ／ 5 + 1 / 5 ／ 7 + 1 / 7 ／ 9 + 1 / 9 ／ 11 + 1 / 11 ／ 13 + 1 / 13 ／ 15 + 1 / 15 ／ 17

1 / 3 + 1 / 5 + 1 / 5 + 1 / 7 + 1 / 7 + 1 / 9 + 1 / 9 + 1 / 11 + 1 / 13 + 1 / 13 + 1 / 15 + 1 / 17 1 ／ 3 + 1 / 3 ／ 5 + 1 / 5 ／ 7 + 1 / 7 ／ 9 + 1 / 9 ／ 11 + 1 / 11 ／ 13 + 1 / 13 ／ 15 + 1 / 15 ／ 17

Solution: 1 / 3 + (1 / 3) / 5 + (1 / 5) / 7 +... (1 / 15) / 17 = 1 / (1 * 3) + 1 / (3 * 5) + 1 / (5 * 7) +... 1 / (15 * 17) = (1 / 2) (1 / 1-1 / 3) + (1 / 2) (1 / 3-1 / 5) + (1 / 2) (1 / 5-1 / 7) +... + (1 / 2) (1 / 15-1 / 17) = (1 / 2) [(1 / 1-1 / 3) + (1 / 3-1 / 5) + (1 / 5-1 /

7 out of 9 * () = 11 out of 13 * () = 5 out of 6 * () = 1
5 / 9 * () = 5 / 9 / () = 5 / 9 + () = 1

5 / 9 * (9 / 5) = 5 / 9 / (5 / 9) = 5 / 9 + (4 / 9) = 1

1 - 3 5 - 7 9 - 11 13————
A2n-1 b1-2n C (- 1) to the power of n (2n-1) d (- 1) to the power of N + 1 (2n-1)

Choose D
If it's not a big one, just take a few numbers,
It is obvious that n = 1,3,3,7 is wrong
B. The sequence brought in is - 1, - 3, - 5, - 7
C. The sequence is - 1,3, - 5,7
D. The number sequence brought in is 1, - 3,5, - 7

1 of 23 + 3 of 23 + 5 of 23 + 7 of 23 + 9 of 23 + 11 of 23 + 13 of 23 + 15 of 23 + 17 of 23 + 19 of 23
Please quickly work out what the above formula equals

100/23
（1/23+19/23）+（3/23+17/23）+（5/23+15/23）…… =20 / 23 times 5 = 100 / 23