Ta có :
\(\dfrac{1}{101}>\dfrac{1}{150}\)
\(\dfrac{1}{102}>\dfrac{1}{150}\)
\(.............\)
\(\dfrac{1}{150}=\dfrac{1}{150}\)
\(\Rightarrow\dfrac{1}{101}+\dfrac{1}{102}+...+\dfrac{1}{150}>\dfrac{1}{150}+\dfrac{1}{150}+...+\dfrac{1}{150}\)( 50 số hạng ) \(=\dfrac{1}{3}\)
Ta có :
\(\dfrac{1}{151}>\dfrac{1}{200}\)
\(\dfrac{1}{152}>\dfrac{1}{200}\)
\(..............\)
\(\dfrac{1}{200}=\dfrac{1}{200}\)
\(\Rightarrow\dfrac{1}{151}+\dfrac{1}{152}+...+\dfrac{1}{200}>\dfrac{1}{200}+\dfrac{1}{200}+...+\dfrac{1}{200}\)( có 50 số hạng ) \(=\dfrac{1}{4}\)
\(\Rightarrow\dfrac{1}{101}+\dfrac{1}{102}+...+\dfrac{1}{200}>\dfrac{1}{3}+\dfrac{1}{4}\)
\(\Rightarrow A>\dfrac{7}{12}\)
잘 공부하십시오 !
