a, \(\left(x-5\right).30\%=\dfrac{20x}{100}+5\Rightarrow\left(x-5\right).\dfrac{3}{10}=\dfrac{x}{5}+5\)
\(\Rightarrow\dfrac{3}{10}x+\dfrac{3}{2}=\dfrac{x}{5}+5\Rightarrow\dfrac{3}{10}x-\dfrac{x}{5}=5-\dfrac{3}{2}\)
\(\Rightarrow x\left(\dfrac{3}{10}-\dfrac{1}{5}\right)=\dfrac{7}{2}\Rightarrow\dfrac{1}{10}x=\dfrac{7}{2}\Rightarrow x=35\)
b, \(\dfrac{x+3}{x-2}\in Z\)
Ta có: \(\dfrac{x-2+5}{x-2}=\dfrac{x-2}{x-2}+\dfrac{5}{x-2}=1+\dfrac{5}{x-2}\)
Để \(\dfrac{x+3}{x-2}\in Z\Leftrightarrow\dfrac{5}{x-2}\Leftrightarrow5⋮\left(x-2\right)\Rightarrow\left(x-2\right)\in U\left(5\right)\)
\(\Rightarrow\left(x-2\right)\in\left\{1;5\right\}\Rightarrow x\in\left\{-1;3\right\}\)
Kiến thức lâu k học :> sai gì bỏ qua giùm :<<
