TÍNH:
a) \(\frac{1}{12}\)+\(\frac{1}{20}\)\(\frac{1}{30}\)+\(\frac{1}{42}\)+\(\frac{1}{56}\)+\(\frac{1}{72}\)+\(\frac{1}{90}\)+\(\frac{1}{110}\)+\(\frac{1}{132}\)
b) (1-\(\frac{1}{7}\)).(1-\(\frac{1}{8}\)).(1-\(\frac{1}{9}\)) .... ( 1-\(\frac{1}{2011}\))
c) ( \(\frac{1}{10}\)-1).(\(\frac{1}{11}\)-1).(\(\frac{1}{12}\)-1) .... ( \(\frac{1}{2012}\)-1)
d) \(\frac{8^2}{7.9}\). \(\frac{9^2}{8.10}\).\(\frac{10^2}{9.11}\).\(\frac{11^2}{10.12}\).\(\frac{12^2}{11.13}\).\(\frac{13^2}{12.14}\).\(\frac{14^2}{13.15}\)
