5.488 Найдите значение выражения: a) 3/7a при a = 3/7, a = 119/66, a = 28/33, a = 1. б) 5/12b при b = 1/5, b = 5/12, b = 6/5, b = 84/25, b = 0.

а) Найдем значение выражения $$\frac{3}{7}a$$ при $$a = \frac{3}{7}$$, $$a = \frac{119}{66}$$, $$a = \frac{28}{33}$$, $$a = 1$$.

При $$a = \frac{3}{7}$$: $$\frac{3}{7} \cdot \frac{3}{7} = \frac{3 \cdot 3}{7 \cdot 7} = \frac{9}{49}$$.

При $$a = \frac{119}{66}$$: $$\frac{3}{7} \cdot \frac{119}{66} = \frac{3 \cdot 119}{7 \cdot 66} = \frac{1 \cdot 17}{1 \cdot 22} = \frac{17}{22}$$.

При $$a = \frac{28}{33}$$: $$\frac{3}{7} \cdot \frac{28}{33} = \frac{3 \cdot 28}{7 \cdot 33} = \frac{1 \cdot 4}{1 \cdot 11} = \frac{4}{11}$$.

При $$a = 1$$: $$\frac{3}{7} \cdot 1 = \frac{3}{7}$$.

б) Найдем значение выражения $$\frac{5}{12}b$$ при $$b = \frac{1}{5}$$, $$b = \frac{5}{12}$$, $$b = \frac{6}{5}$$, $$b = \frac{84}{25}$$, $$b = 0$$.

При $$b = \frac{1}{5}$$: $$\frac{5}{12} \cdot \frac{1}{5} = \frac{5 \cdot 1}{12 \cdot 5} = \frac{1 \cdot 1}{12 \cdot 1} = \frac{1}{12}$$.

При $$b = \frac{5}{12}$$: $$\frac{5}{12} \cdot \frac{5}{12} = \frac{5 \cdot 5}{12 \cdot 12} = \frac{25}{144}$$.

При $$b = \frac{6}{5}$$: $$\frac{5}{12} \cdot \frac{6}{5} = \frac{5 \cdot 6}{12 \cdot 5} = \frac{1 \cdot 1}{2 \cdot 1} = \frac{1}{2}$$.

При $$b = \frac{84}{25}$$: $$\frac{5}{12} \cdot \frac{84}{25} = \frac{5 \cdot 84}{12 \cdot 25} = \frac{1 \cdot 7}{1 \cdot 5} = \frac{7}{5} = 1\frac{2}{5}$$.

При $$b = 0$$: $$\frac{5}{12} \cdot 0 = 0$$.

Ответ: а) $$\frac{9}{49}$$, $$\frac{17}{22}$$, $$\frac{4}{11}$$, $$\frac{3}{7}$$; б) $$\frac{1}{12}$$, $$\frac{25}{144}$$, $$\frac{1}{2}$$, $$1\frac{2}{5}$$, $$0$$