a) $$\frac{4}{5}\sqrt{75}+\sqrt{2}(\sqrt{8}-\sqrt{24})$$
Упростим выражение:
$$\frac{4}{5}\sqrt{75}+\sqrt{2}(\sqrt{8}-\sqrt{24}) = \frac{4}{5}\sqrt{25\cdot3}+\sqrt{2}(\sqrt{4\cdot2}-\sqrt{4\cdot6}) = \frac{4}{5}\cdot5\sqrt{3}+\sqrt{2}(2\sqrt{2}-2\sqrt{6}) = 4\sqrt{3}+2\sqrt{2}\cdot\sqrt{2}-2\sqrt{2}\cdot\sqrt{6} = 4\sqrt{3}+2\cdot2-2\sqrt{12} = 4\sqrt{3}+4-2\sqrt{4\cdot3} = 4\sqrt{3}+4-2\cdot2\sqrt{3} = 4\sqrt{3}+4-4\sqrt{3} = 4$$
б) $$\left(\sqrt{8}-\sqrt{5}\right)^2$$
Упростим выражение:
$$(\sqrt{8}-\sqrt{5})^2 = (\sqrt{8})^2 - 2\sqrt{8}\sqrt{5} + (\sqrt{5})^2 = 8 - 2\sqrt{40} + 5 = 13 - 2\sqrt{4\cdot10} = 13 - 2\cdot2\sqrt{10} = 13 - 4\sqrt{10}$$
Ответ: a) 4; б) $$13 - 4\sqrt{10}$$