а) \(\frac{3}{5} \cdot \frac{4}{9} = \frac{3 \cdot 4}{5 \cdot 9} = \frac{12}{45} = \frac{4}{15}\)
б) \(\frac{7}{9} : \frac{21}{25} = \frac{7}{9} \cdot \frac{25}{21} = \frac{7 \cdot 25}{9 \cdot 21} = \frac{175}{189} = \frac{25}{27}\)
в) \((\frac{3}{4})^2 = \frac{3}{4} \cdot \frac{3}{4} = \frac{9}{16}\)