Задание 4. Найдите значение выражения: 1) 1/(1/30 + 1/42); 2) 1/(1/36 − 1/44); 3) 1/(1/36 + 1/45); 4) 1/(1/35 − 1/60); 5) 1/(1/21 + 1/28); 6) 1/(1/72 − 1/99).

1. \(\frac{1}{\frac{1}{30}+\frac{1}{42}}=\frac{1}{\frac{7+5}{210}}=\frac{210}{12}=\frac{35}{2}\).
2. \(\frac{1}{\frac{1}{36}-\frac{1}{44}}=\frac{1}{\frac{44-36}{1584}}=\frac{1584}{8}=198\).
3. \(\frac{1}{\frac{1}{36}+\frac{1}{45}}=\frac{1}{\frac{5+4}{180}}=20\).
4. \(\frac{1}{\frac{1}{35}-\frac{1}{60}}=\frac{1}{\frac{60-35}{2100}}=\frac{2100}{25}=84\).
5. \(\frac{1}{\frac{1}{21}+\frac{1}{28}}=\frac{1}{\frac{4+3}{84}}=12\).
6. \(\frac{1}{\frac{1}{72}-\frac{1}{99}}=\frac{1}{\frac{99-72}{7128}}=\frac{7128}{27}=264\).

Ответ: 1) \(\frac{35}{2}\); 2) \(198\); 3) \(20\); 4) \(84\); 5) \(12\); 6) \(264\).