[tex]\sqrt{7-4\sqrt{3}} + \sqrt{7+4\sqrt{3}} = \\ \\
=\sqrt{4+3-4\sqrt{3}} + \sqrt{4+3+4\sqrt{3}} = \\ \\
=\sqrt{4-4\sqrt{3}+3} + \sqrt{4+4\sqrt{3}+3} = \\ \\
=\sqrt{2^2+2\times 2\times (-\sqrt{3})+(- \sqrt{3} )^2} + \sqrt{2^2+2\times 2\times \sqrt{3}+(\sqrt{3})^2} = \\ \\
= \sqrt{(2-\sqrt{3})^2} + \sqrt{(2+\sqrt{3})^2} =2-\sqrt{3} +2+\sqrt{3} =2+2=\boxed{4\in N}[/tex]