Question

tính hợp lý 

,A=\(\frac{1}{56}\)+\(\frac{1}{72}\)+\(\frac{1}{90}\)+\(\frac{1}{110}\)+\(\frac{1}{132}\)+\(\frac{1}{156}\)

Answer 1

\(A=\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}+\frac{1}{132}+\frac{1}{156}\)

\(=\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}+\frac{1}{10.11}+\frac{1}{11.12}+\frac{1}{12.13}\)

\(=\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}+\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}+\frac{1}{12}-\frac{1}{13}\)

\(=\frac{1}{7}-\frac{1}{13}\)

\(=\frac{6}{91}\)

Answer 2

\(A=\frac{1}{7\times8}+\frac{1}{8\times9}+\frac{1}{9\times10}+...+\frac{1}{13\times14}\)

\(=\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+...+\frac{1}{13}-\frac{1}{14}\)

\(=\frac{1}{7}-\frac{1}{14}=\frac{1}{14}\)

Answer 3

Mk nhầm nha!

\(A=\frac{1}{56}+\frac{1}{72}+...+\frac{1}{156}\)

\(=\frac{1}{7\times8}+\frac{1}{8\times9}+...+\frac{1}{12\times13}\)

\(=\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+...+\frac{1}{12}-\frac{1}{13}\)

\(=\frac{1}{7}-\frac{1}{13}=\frac{13-7}{91}=\frac{6}{91}\)

Answer 4

\(=\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+........\frac{1}{13}-\frac{1}{14}=\frac{1}{7}-\frac{1}{14}=\frac{1}{14}\)

~Study well~ :)

(*Mk ko ghi đề đâu nhé)

Answer 5

\(A=\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}+\frac{1}{132}+\frac{1}{156}\)

\(A=\frac{1}{7\cdot8}+\frac{1}{8\cdot9}+\frac{1}{9\cdot10}+\frac{1}{10\cdot11}+\frac{1}{11\cdot12}+\frac{1}{12\cdot13}\)

\(A=\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}+\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}+\frac{1}{12}-\frac{1}{13}\)

\(A=\frac{1}{7}-\frac{1}{13}\)

\(A=\frac{6}{91}\)