Berapa hasil dari {akar (21+8 akar(5))}

[tex] \sqrt{21 + 8 \sqrt{5} } \\ = \sqrt{21 + 2 \sqrt{80} } \\ = \sqrt{16 + 2 \sqrt{16 + \times 5} + 5} \\ = \sqrt{( \sqrt{16} + \sqrt{5}) ^{2} } \\ = \sqrt{16} + \sqrt{5} \\ = 4 + \sqrt{5} [/tex]