Question

[Nguyễn Thị Khánh Ngọc]

giúp mình nhá, khó ghê

Answer 1

[Lê Khánh Linh]

\(A=\frac{2}{5.7}+\frac{4}{7.11}+\frac{2}{11.13}+\frac{4}{13.17}+\frac{2}{17.19}+\frac{4}{19.23}+\frac{2}{23.25}\)

\(A=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+...+\frac{1}{23}-\frac{1}{25}\)

\(A=\frac{1}{5}-\frac{1}{25}\)

\(A=\frac{4}{25}\)

\(B=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}\)

\(B=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+....+\frac{1}{8}-\frac{1}{9}\)

\(B=1-\frac{1}{9}\)

\(B=\frac{8}{9}\)