Question

Bài 3 đề Bài 3 đề 1 !! Giúp mình nhé

Answer 1

Bài 3:
\(A=\frac{3}{11.16}+\frac{3}{16.21}+\frac{3}{21.26}+...+\frac{3}{61.66}\)

\(\Rightarrow A=3.\left(\frac{1}{11.16}+\frac{1}{16.21}+\frac{1}{21.26}+...+\frac{1}{61.66}\right)\)

\(\Rightarrow A=\frac{3}{5}.\left(\frac{5}{11.16}+\frac{5}{16.21}+\frac{5}{21.26}+...+\frac{5}{61.66}\right)\)

\(\Rightarrow A=\frac{3}{5}.\left(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}+...+\frac{1}{61}-\frac{1}{66}\right)\)

\(\Rightarrow A=\frac{3}{5}.\left(\frac{1}{11}-\frac{1}{66}\right)\)

\(\Rightarrow A=\frac{3}{5}.\frac{5}{66}\)

\(\Rightarrow A=\frac{1}{22}\)

Vậy \(A=\frac{1}{22}\)