Tính:
A= \(\frac{1}{2.9}\)+ \(\frac{1}{9.7}\)+\(\frac{1}{7.19}\)+...+\(\frac{1}{252.509}\)
B= \(\frac{1}{10.9}\)+\(\frac{1}{18.13}\)+\(\frac{1}{26.17}\)+...+\(\frac{1}{802.405}\)
C= \(\frac{2}{4.7}\)- \(\frac{3}{5.9}\)+\(\frac{2}{7.10}\)- \(\frac{3}{9.13}\)+...+\(\frac{2}{301.304}\)- \(\frac{3}{401.405}\)