Đặt \(A=\dfrac{1}{2^2}+\dfrac{1}{3^2}+...+\dfrac{1}{200^2}\)
=>\(A< \dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+...+\dfrac{1}{199\cdot200}\)
=>\(A< 1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{199}-\dfrac{1}{200}\)
=>\(A< 1-\dfrac{1}{200}=\dfrac{199}{200}< 1\)