Ответ:

  1. \(\sqrt{a+b}=\sqrt{-0.27+0.63}=\sqrt{0.36}=0.6\).
  2. \(\sqrt{a+b}=\sqrt{\frac{3}{4}+\frac{1}{18}}=\sqrt{\frac{27}{36}+\frac{2}{36}}=\sqrt{\frac{29}{36}}=\frac{\sqrt{29}}{6}\).

Ответ: 1) 0,6; 2) \(\frac{\sqrt{29}}{6}\).