[tex] \frac{7}{3- \sqrt{2}}= \frac{7(3+ \sqrt{2})}{(3- \sqrt{2})(3+ \sqrt{2})} -> am amplificate fractia cu conjugatul (3+[tex] \sqrt{2} [/tex])
De aici,prin formula (a+b)(a-b)=[tex] a^{2}+ b^{2} [/tex] se obtine :
[tex] \frac{7(3+ \sqrt{2})}{ 3^{2}- \sqrt{2} ^{2} } = \frac{7(3+ \sqrt{2})}{9-2} = \frac{7(3+ \sqrt{2})}{7} = 3+ \sqrt{2} [/tex]
