N=3/2.(1/5.7+1/7.9+1/9.11+....+1/197.199)
N=3/2.(1/5-1/7+1/7-1/9+1/9-1/11+....+1/197-1/199)
N=3/2.(1/5-1/199)
N=3/2.194/995
N=291/995
Có N = 3 . (1/5 . 7 + 1/7 . 9 + .... + 1/197 . 199)
2N = 3 . (2/5 . 7 + 2/7 . 9 + ... + 2/197 . 199)
2N = 3 . (1/5 - 1/7 + 1/7 - 1/9 + ... + 1/197 - 1/199)
2N = 3 . (1/5 - 1/199)
N = \(\frac{3.\left(\frac{1}{5}-\frac{1}{199}\right)}{2}\)
N = (3 . 194/995) : 2
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