Verified answer

[tex]\displaystyle\bf\\x=1,6\\\\y=0,4\\\\\\\sqrt{2x-8y} =\sqrt{2\cdot(x-4y)}=\sqrt{2\cdot(1,6-4\cdot 0,4)} =\\\\=\sqrt{2\cdot(1,6-1,6)} =\sqrt{2\cdot 0}=0[/tex]