Question

[TXT Channel Funfun]

Cho \(A=\frac{1}{2}-\frac{1}{3}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{48}-\frac{1}{49}\)

CMR : \(\frac{1}{5}< A< \frac{2}{5}\)

Answer 1

[Hoàng Phú Huy]

=1−12 +13 −14 +15 −16 +...+149 −150. A =(1+13 +15 +...+149 )−(12 +14 +16 +...+150 ).

A =(1+12 +13 +14 +15 +16 +...+149 ...

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