[tex]F_1=35 \ N \\ \triangle l _1=5 \ cm=0,05 \ m \\ F_2=7 \ N \\ F_3=63 \ N \\ \triangle l_2-? \\ \triangle l_3-? \\ \boxed{k= \frac{F}{\triangle l} } \Rightarrow \triangle l_2= \frac{F_2}{k} , \ iar \ \triangle l_3= \frac{F_3}{k} \\ k= \frac{F_1}{\triangle l_1} \Rightarrow k= \frac{35 \ N}{0,05 \ m} \\ k=700 \ N/m \\ \Rightarrow \triangle l_2= \frac{7 \ N}{700 \ N/m} \\ \boxed{ \triangle l_2=0,01 \ m}; \\ \Rightarrow \triangle l_3= \frac{63 \ N}{700 \ N/m} \\ \boxed{ \triangle l_3=0,09 \ m}.[/tex]
