Tìm x biết:
a) \(\frac{1}{5\cdot8}\) + \(\frac{1}{8\cdot11}\) + \(\frac{1}{11\cdot14}\) + .....+ \(\frac{1}{x\cdot\left(x+3\right)}\) = \(\frac{101}{1540}\)
b) \(1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{1}{x\cdot\left(x+1\right):2}=1\frac{1991}{1993}\)