x=
[tex] \frac{9}{ \sqrt{28} } - \frac{1}{ \sqrt{7} ?} = \frac{9}{2 \sqrt{7} ?} - \frac{ \sqrt{7} }{7} = \frac{9 \sqrt{7} }{14} - \frac{ \sqrt{7} }{7} = \frac{ \sqrt{7} }{2}
y=
\frac{7}{ 3} ( \frac{5}{2 \sqrt{7} } + \frac{8}{ \sqrt{7} } ) = \frac{7}{3} \times \frac{21}{2 \sqrt{7} } = 7 \times \frac{7}{2 \sqrt{7} } = \frac{49}{2 \sqrt{7} } = \frac{7 \sqrt{7} }{2} [/tex]
