Giải thích các bước giải:
$A=\dfrac{1}{2^2}+\dfrac{1}{2^4}+\dfrac{1}{2^6}+...+\dfrac{1}{2^{100}}\\ \rightarrow \dfrac{1}{2^2}A=\dfrac{1}{2^4}+\dfrac{1}{2^6}+\dfrac{1}{2^8}+...+\dfrac{1}{2^{102}}\\ \rightarrow A-\dfrac{1}{2^2}A=\dfrac{1}{2^2}-\dfrac{1}{2^{102}}\\ \rightarrow \dfrac{3}{4}A=\dfrac{1}{4}-\dfrac{1}{2^{102}}\\ \rightarrow \dfrac{3}{4}A<\dfrac{1}{4}\\ \rightarrow A<\dfrac{1}{3}$
