Question

найдите значения выражений 1/ 1/30 + 1/42

Answer 1

 frac{1}{ frac{1}{30} + frac{1}{42} } = frac{1}{frac{1}{5*6} + frac{1}{6*7}}  = 
frac{1}{frac{7 + 5}{5*6*7}} = frac{1}{frac{12}{5*6*7}} = 
frac{1}{frac{2}{5*7}} = frac{1}{frac{2}{35}} = frac{35}{2}