Tính :
a) \(\frac{2}{6}\) + \(\frac{2}{12}\)+ \(\frac{2}{20}\)+ \(\frac{2}{30}\)+...+ \(\frac{2}{90}\)+ \(\frac{2}{110}\)
b) \(1\)- \(\frac{1}{2}\)- \(\frac{1}{4}\)-\(\frac{1}{8}\)- \(\frac{1}{16}\)- \(\frac{1}{32}\)- .........- \(\frac{1}{1024}\)- \(\frac{1}{2048}\)
Cảm ơn nhiều ^^