Răspuns:
19/7
Explicație pas cu pas:
[tex]2,1(6)=2\dfrac{16-1}{90}=2\dfrac{15}{90}=2\dfrac{1}{6}=\dfrac{2*6+1}{6}=\dfrac{13}{6}\\ Deci \dfrac{x}{y}= \dfrac{13}{6}~=>~\dfrac{x}{13}=\dfrac{y}{6} =k\\[/tex]
⇒x=13k, y=6k.
Atunci, (x+y)/(x-y)=(13k+6k)/(13k-6k)=(19·k)/(7·k)=19/7.
