\[\boxed{\mathbf{529\ (529).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ 4\sqrt{a} + 3\sqrt{a} - 5\sqrt{a} =\]
\[= \sqrt{a} \cdot (4 + 3 - 5) = 2\sqrt{a};\]
\[2)\ 6\sqrt{b} + 2\sqrt{b} - 8\sqrt{b} =\]
\[= \sqrt{b} \cdot (6 + 2 - 8) = 0;\]
\[3)\ 5\sqrt{c} + 3\sqrt{d} - \sqrt{c} + 3\sqrt{d} =\]
\[= 4\sqrt{c} + 6\sqrt{d};\]
\[4)\ \sqrt{5} + 7\sqrt{5} - 4\sqrt{5} = 4\sqrt{5}.\]