4.
[tex]A = \frac{ {20}^{2} - {16}^{2} }{ {3}^{2} } + \frac{ {12}^{2} + {9}^{2} }{ {5}^{2} } = \\ \frac{ 400 - 256 }{ 9 } + \frac{ 144 +81 }{ 25} = \\ \frac{144}{9} + \frac{225}{25} = \\ 16 + 9 = 25[/tex]
[tex] \sqrt{A} = \sqrt{25} = 5[/tex]
5.
[tex]B = \sqrt{ \frac{16}{9} } + \sqrt{ \frac{25}{9} } - \sqrt{36} + \sqrt{64} \\ = \frac{ \sqrt{16} }{ \sqrt{9} } + \frac{ \sqrt{25} }{ \sqrt{9} } - 6 + 8 = \\ \frac{4}{3} + \frac{5}{3} - 6 + 8 = \\ \frac{9}{3} - 6 + 8 = \\ 3 - 6 + 8 = - 3 + 8 = 5[/tex]
