GIÚP MK VS NHA >-<
Tính Tổng:
a) $\frac{1}{1X2}$+ $\frac{1}{2X3}$ +...+$\frac{1}{101X102}$
b) $\frac{2}{1X3}$+ $\frac{2}{3X5}$+...+ $\frac{2}{49X51}$
c) $\frac{3}{3X8}$ + $\frac{3}{8X13}$+...+ $\frac{3}{103X108}$
d)$\frac{2}{4X7}$+ $\frac{2}{7X10}$+...+ $\frac{2}{124X127}$