[tex] \sqrt{6.4} = \frac{4 \sqrt{10} }{5} [/tex]
[tex] \sqrt{6.4} = \sqrt{ \frac{32}{5} } = \frac{ \sqrt{32} }{ \sqrt{5} } [/tex]
[tex] \frac{ \sqrt{32} }{ \sqrt{5} } = \sqrt{32} = \sqrt{ {4}^{2} } \times 2 = \sqrt{ {4}^{2} } \sqrt{2} [/tex]
[tex] \sqrt{ {4}^{2} } \sqrt{2} = \sqrt{ {4}^{2} } = 4 = 4 \sqrt{2} [/tex]
[tex] = [/tex]
[tex] \frac{ \sqrt{32} }{ \sqrt{5} } = \frac{4 \sqrt{2} }{ \sqrt{5} } [/tex]
[tex] \frac{4 \sqrt{2} }{ \sqrt{5} } = \frac{4 \sqrt{2} \sqrt{5} }{ \sqrt{5} \sqrt{5} } = \frac{4 \sqrt{10} }{5} [/tex]
