\[Страница\ 113.\]
\[\boxed{\mathbf{7.}}\]
\[\textbf{а)}\ \ 58\ :208 = \frac{1}{2}\ :7\]
\[58 \cdot 7 = 406\]
\[208 \cdot \frac{1}{2} = 104\]
\[406 \neq 104 \Longrightarrow неверно.\]
\[\textbf{б)}\ \frac{11,6}{1,2} = \frac{2,9}{0,3}\]
\[11,6 \cdot 0,3 = 3,48\]
\[1,2 \cdot 2,9 = 3,48\]
\[3,48 = 3,48 \Longrightarrow верно.\]
\[Ответ:а)\ нет;\ \ б)\ да.\]
\[\boxed{\mathbf{8.}}\]
\[\textbf{а)}\ 5\ :25 = 3\ :15\]
\[5\ :3 = 25\ :15\]
\[15\ :25 = 3\ :5\]
\[15\ :3 = 25\ :5\]
\[\textbf{б)}\ 3,4\ :1,25 = 0,4\ :\frac{5}{34}\]
\[3,4\ :0,4 = 1,25\ :\frac{5}{34}\]
\[\frac{5}{34}\ :1,25 = 0,4\ :3,4\]
\[\frac{5}{34}\ :0,4 = 1,25\ :3,4\]
\[\textbf{в)}\ 2\ :3 = b\ :a\]
\[2\ :b = 3\ :a\]
\[a\ :3 = b\ :2\]
\[a\ :b = 3\ :2\]
\[\textbf{г)}\ a\ :m = n\ :b\]
\[a\ :n = m\ :b\]
\[b\ :m = n\ :a\]
\[b\ :n = m\ :a\]
\[\textbf{д)}\ \ x\ :a = b\ :x\]
\[x\ :b = a\ :x\]
\[a\ :x = x\ :b\]
\[b\ :x = x\ :a\]
\[\boxed{\mathbf{9.}}\]
\[\textbf{а)}\ 3\ :9 = 4\ :12\]
\[\textbf{б)}\ 12\ :4 = 9\ :3\]
\[\textbf{в)}\ 12\ :9 = 4\ :3\]