Question

b=9/4=9/28+9/70+9/130

Answer 1

Sửa đề: \(b=\frac94+\frac{9}{28}+\frac{9}{70}+\frac{9}{130}\)

\(=\frac{9}{1\times4}+\frac{9}{4\times7}+\frac{9}{7\times10}+\frac{9}{10\times13}\)

\(=3\times\left(\frac{3}{1\times4}+\frac{3}{4\times7}+\frac{3}{7\times10}+\frac{3}{10\times13}\right)\)

\(=3\times\left(1-\frac14+\frac14-\frac17+\frac17-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}\right)=3\times\left(1-\frac{1}{13}\right)=3\times\frac{12}{13}=\frac{36}{13}\)