Question

1/4 + 1/12 + 1/24 + 1/40 + 1/60 + 1/84

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Answer 1

\(\frac{1}{4}+\frac{1}{12}+\frac{1}{24}+\frac{1}{40}+\frac{1}{60}+\frac{1}{84}=\frac{12}{7}\)

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Answer 2

đặt A =1/4+...+1/84

A=2/8 +2/24+...+2/168

A=2/2.4+2/4.6+...+2/12.14

A=1/2-1/4+1/4-1/6 +...+1/12-1/14

A=1/2-1/14

A=6/14=3/7

Answer 3

\(\frac{1}{4}+\frac{1}{12}+\frac{1}{24}+\frac{1}{40}+\frac{1}{60}+\frac{1}{84}\)

\(=\left(\frac{1}{4}+\frac{1}{12}\right)+\left(\frac{1}{24}+\frac{1}{40}\right)+\left(\frac{1}{60}+\frac{1}{84}\right)\)

\(=\frac{1}{3}+\frac{1}{15}+\frac{1}{35}=\frac{3}{7}\)