a) \(2\sqrt{7} = \sqrt{2^2\cdot7} = \sqrt{4\cdot7} = \sqrt{28}\)
б) \(3\sqrt{\frac{1}{3}} = \sqrt{3^2\cdot\frac{1}{3}} = \sqrt{9\cdot\frac{1}{3}} = \sqrt{3}\)
в) \(-\frac{4}{5}\sqrt{75} = -\frac{4}{5}\sqrt{25\cdot3} = -\frac{4}{5}\cdot5\sqrt{3} = -4\sqrt{3} = -\sqrt{16\cdot3} = -\sqrt{48}\)