Bài 1: Tính
A=\(\left(\dfrac{3}{7}-\dfrac{3}{17}+\dfrac{3}{37}\right):\left(\dfrac{5}{7}-\dfrac{5}{17}+\dfrac{5}{37}\right)+\dfrac{2}{5}\)
Bài 2: So sánh B với \(\dfrac{1}{2}\) biết:
B= \(\dfrac{1}{3}+\dfrac{1}{3^2}+\dfrac{1}{3^3}+...+\dfrac{1}{3^{100}}\)