[tex] \frac{ \sqrt{5} }{7} + \frac{ \sqrt{6} }{9} = \frac{1}{63} \times (9 \sqrt{5} + 7 \sqrt{6} )[/tex]
[tex] \sqrt{ \frac{5}{7} } + \sqrt{ \frac{6}{9} } = \frac{ \sqrt{5} }{ \sqrt{7} } + \frac{ \sqrt{6} }{3} = \frac{ \sqrt{35} }{7} + \frac{ \sqrt{6} }{3} [/tex]
sau
[tex] \sqrt{ \frac{5}{7} } + \sqrt{ \frac{6}{9} } = \sqrt{ \frac{1}{63} } ( \sqrt{45} + \sqrt{42}) = \sqrt{ \frac{1}{63} } (3 \sqrt{5} + \sqrt{42} )[/tex]
