Rút gọn các biểu thức sau:
a) A = 1 + \(\dfrac{1}{3}\) + \(\dfrac{1}{3^2}\) + \(\dfrac{1}{3^3}\) +...+ \(\dfrac{1}{3^n}\)
b) B = \(\dfrac{1}{2}\) - \(\dfrac{1}{2^2}\) + \(\dfrac{1}{2^3}\) - \(\dfrac{1}{2^4}\) +...+ \(\dfrac{1}{2^{99}}\) - \(\dfrac{1}{2^{100}}\)
c) C = \(\dfrac{3}{2^2}\) x \(\dfrac{8}{3^2}\) x \(\dfrac{15}{4^2}\) ... \(\dfrac{899}{30^2}\)
(Mình cần gấp ạ)