а) \(3\sqrt{81}-\frac{1}{2}\sqrt{36}\); б) \(\sqrt{1\frac{9}{16}}+\frac{2}{7}\sqrt{0,49}\).

а)

\(\sqrt{81}=9\), \(\sqrt{36}=6\).

\(3\sqrt{81}-\frac{1}{2}\sqrt{36}=3\cdot9-\frac{1}{2}\cdot6=27-3=24\).

б)

\(1\frac{9}{16}=\frac{25}{16}\), поэтому \(\sqrt{1\frac{9}{16}}=\frac{5}{4}\). Также \(\sqrt{0.49}=0.7=\frac{7}{10}\).

\(\sqrt{1\frac{9}{16}}+\frac{2}{7}\sqrt{0.49}=\frac{5}{4}+\frac{2}{7}\cdot\frac{7}{10}=\frac{5}{4}+\frac{1}{5}=\frac{25}{20}+\frac{4}{20}=\frac{29}{20}=1\frac{9}{20}\).

Ответ: а) 24; б) \(\frac{29}{20}=1\frac{9}{20}\).