Question

[trieu tien hung]

1/3+1/6+1/10+1/15+1/21+1/28

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Answer 1

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Tính

Đặt \(Q=\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+\frac{1}{28}\)

\(\Rightarrow\frac{1}{2}\times Q=\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}\)

\(=\frac{1}{2\times3}+\frac{1}{3\times4}+\frac{1}{4\times5}+\frac{1}{5\times6}+\frac{1}{6\times7}+\frac{1}{7\times8}\)

\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}\)

\(=\frac{1}{2}-\frac{1}{8}=\frac{4}{8}-\frac{1}{8}=\frac{3}{8}\)

\(\Rightarrow Q=\frac{3}{8}:\frac{1}{2}=\frac{3}{8}\times2=\frac{3}{4}\)

Vậy \(Q=\frac{3}{4}.\)

Answer 2

[꧁༺Douma Thượng Huyền Nhị(ɻɛɑm ʙáo c...]

3/4

HT