Question

\(\frac{4}{1.2.5}+\frac{4}{3.5.7}+\frac{4}{5.7.9}+\frac{4}{7.9.11}+\frac{4}{9.11.13}\)

    tính

Answer 1

=1/1.3-1/3.5+1/3.5-1/5.7+...+1/99.11-1/11.13

=1/1.3-1/11.13

=1/3-1/143

=140/429