Question

2/3.5+3/5.8+......+16/122.138

Answer 1

Ta có: \(\dfrac{2}{3\cdot5}+\dfrac{3}{5\cdot8}+...+\dfrac{16}{122\cdot138}\)

\(=\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+...+\dfrac{1}{122}-\dfrac{1}{138}\)

\(=\dfrac{1}{3}-\dfrac{1}{138}\)

\(=\dfrac{46}{138}-\dfrac{1}{138}\)

\(=\dfrac{45}{138}=\dfrac{15}{46}\)

Answer 2

Giải:

2/3.5+3/5.8+...+16/122.138

=1/3-1/5+1/5-1/8+...+1/122-1/138

=1/3-1/138

=45/138=15/46

Chúc bạn học tốt!