a) $$\frac{25}{64} = (\frac{5}{8})^2 = 0.390625$$
б) $$\sqrt{56} \cdot \sqrt{14} = \sqrt{56 \cdot 14} = \sqrt{784} = 28$$
в) $$2 \cdot (\sqrt{3})^2 = 2 \cdot 3 = 6$$
Ответ: a) 0.390625; б) 28; в) 6