Tính tổng:
a) A=\(\left(1-\frac{1}{2}\right)\)\(\left(1-\frac{1}{3}\right)\)\(\left(1-\frac{1}{3}\right)\)........\(\left(1-\frac{1}{100}\right)\)
b) B=\(\frac{1}{1.2}\)+ \(\frac{1}{2.3}\)+ \(\frac{1}{3.4}\)+ .... +\(\frac{1}{2014.2015}\)
c) C=\(\frac{2}{3.5}\)+ \(\frac{2}{5.7}\)+ .... +\(\frac{2}{97.99}\)
d. D=\(\frac{2}{1.4}\)+ \(\frac{2}{4.7}\)+ ..... +\(\frac{2}{2012.2015}\)