Question

[NGUYỄN THỊ THANH MAI]

Tính già trị biểu thức:

\(A=\dfrac{6}{8}+\dfrac{6}{56}+\dfrac{6}{140}+...+\dfrac{6}{1100}+\dfrac{6}{1400}\)

Answer 1

[Hoàng Hà Nhi]

\(A=\dfrac{3}{4}+\dfrac{3}{28}+\dfrac{3}{140}+...+\dfrac{3}{550}+\dfrac{3}{700}\)

\(A=\dfrac{3}{1.4}+\dfrac{3}{4.7}+\dfrac{3}{7.10}+...+\dfrac{3}{22.25}+\dfrac{3}{25.28}\)

\(A=1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+...+\dfrac{1}{22}-\dfrac{1}{25}+\dfrac{1}{25}-\dfrac{1}{28}\)

\(A=1-\dfrac{1}{28}\)

\(A=\dfrac{28}{28}-\dfrac{1}{28}=\dfrac{27}{28}\)

Answer 2

[Trần Minh An]

vãi