1. Có: \(\dfrac{x}{7}+\dfrac{1}{y}=-\dfrac{1}{14}\)
\(\Rightarrow\dfrac{2x-1}{14}=\dfrac{1}{y}\Rightarrow\left(2x-1\right)y=14\)
Vì \(x,y\in Z\) nên \(2x-1\) phải lẻ
\(\Rightarrow14=1.14=7.2\)
Tới đây lập bảng là xg
2. Có: \(A=1+\dfrac{1}{2}+\left(\dfrac{1}{3}+\dfrac{1}{4}\right)+\left(\dfrac{1}{5}+\dfrac{1}{6}+\dfrac{1}{7}+\dfrac{1}{8}\right)+...+\left(\dfrac{1}{33}+\dfrac{1}{34}+...+\dfrac{1}{63}\right)\)\(\Rightarrow A>1+\dfrac{1}{2}+\dfrac{1}{4}.2+\dfrac{1}{8}.4+...+\dfrac{1}{63}.31\)
\(\Rightarrow A>1+\dfrac{1}{2}+\dfrac{1}{2}+\dfrac{1}{2}+\dfrac{1}{2}+\dfrac{1}{2}+\dfrac{31}{63}\)
\(\Rightarrow A>1+\dfrac{5}{2}+\dfrac{31}{63}=\dfrac{7}{2}+\dfrac{31}{63}>3\)
giải gấp giúp mình vs, mình cảm ơn
