\(A=\dfrac{2}{5\times7}+\dfrac{2}{7\times9}+...+\dfrac{2}{97\times99}\)\(=\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+...+\dfrac{1}{97}-\dfrac{1}{99}\)\(=\dfrac{1}{5}-\dfrac{1}{99}=\dfrac{94}{495}\)Câu trả lời: \(A=\dfrac{2}{5\times7}+\dfrac{2}{7\times9}+...+\dfrac{2}{97\times99}\)\(=\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+...+\dfrac{1}{97}-\dfrac{1}{99}\)\(=\dfrac{1}{5}-\dfrac{1}{99}=\dfrac{94}{495}\)