Question

1 . 

a) 1/2 + 1/6 + 1/12 +....+1/x.(x+1) = 99/100

Answer 1

Giải:

1/2 + 1/6 + 1/12 + ... + 1/x.(x+1) = 99/100

=>1/1.2 + 1/2.3 + 1/3.4 + ... + 1/x.(x+1) = 99/100

1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/x - 1/x+1 = 99/100

1/1 - 1/x+1 = 99/100

        1/x+1 = 1/1 - 99/100

        1/x+1 = 1/100

=>x+1 = 100

        x = 100 - 1

        x = 99

Vậy ...

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