[tex]\dfrac{3}{\sqrt 7- \sqrt 2}\\\\\\=\dfrac{3 \left( \sqrt 7+ \sqrt 2\right)}{\left(\sqrt 7- \sqrt 2 \right)\left( \sqrt 7+\sqrt 2\right)}\\\\\\=\dfrac{3 \left( \sqrt 7+ \sqrt 2\right)}{\left(\sqrt 7 \right)^2 - \left(\sqrt 2 \right)^2 }\\\\\\= \dfrac{3 \left( \sqrt 7+ \sqrt 2\right)}{7-2}\\\\\\=\dfrac{3 \left( \sqrt 7+ \sqrt 2\right)}5[/tex]
