Question

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5 giúp mik nha , mí bn làm đc bài nào thì lm miễn sao giúp chút ít cho mik là đc

Answer 1

2. \(A=\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}+\dfrac{1}{72}+\dfrac{1}{90}+\dfrac{1}{110}+\dfrac{1}{132}\)

\(A=\dfrac{1}{5.6}+\dfrac{1}{6.7}+\dfrac{1}{7.8}+\dfrac{1}{8.9}+\dfrac{1}{9.10}+\dfrac{1}{10.11}+\dfrac{1}{11.12}\)

\(A=\left(\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+...+\dfrac{1}{11}-\dfrac{1}{12}\right)\)

\(A=\dfrac{1}{5}-\dfrac{1}{12}=\dfrac{7}{60}\)

Vậy...

Answer 2

Mình giải cho bạn bài 2 và 4 nhé

2.

\(A=\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}+\dfrac{1}{72}+\dfrac{1}{90}+\dfrac{1}{110}+\dfrac{1}{132}\)\(A=\dfrac{1}{5.6}+\dfrac{1}{6.7}+\dfrac{1}{7.8}+\dfrac{1}{8.9}+\dfrac{1}{9.10}+\dfrac{1}{9.11}+\dfrac{1}{11.12}\)\(A=\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}+...+\dfrac{1}{11}-\dfrac{1}{12}\)\(A=\dfrac{1}{5}-\dfrac{1}{12}\)

\(A=\dfrac{7}{60}\)

4. \(M=\dfrac{20}{112}+\dfrac{20}{280}+\dfrac{20}{520}+\dfrac{20}{832}\)

\(M=\dfrac{20}{8.14}+\dfrac{20}{14.20}+\dfrac{20}{20.26}+\dfrac{20}{26.32}\)

\(M=\dfrac{20}{6}\left(\dfrac{1}{8}-\dfrac{1}{14}+\dfrac{1}{14}-\dfrac{1}{20}+\dfrac{1}{20}-\dfrac{1}{26}+\dfrac{1}{26}-\dfrac{1}{32}\right)\)\(M=\dfrac{20}{6}\left(\dfrac{1}{8}-\dfrac{1}{32}\right)\)

\(M=\dfrac{20}{6}\cdot\dfrac{3}{32}\)

\(M=\dfrac{5}{16}\)

Answer 3

Answer 4

Answer 5

Answer 6

Answer 7

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