[tex] \frac{1}{ \sqrt{6} + \sqrt{7} } = \frac{ \sqrt{6} - \sqrt{7} }{( \sqrt{6} + \sqrt{7} )( \sqrt{6} - \sqrt{7}) } = \frac{ \sqrt{6} - \sqrt{7} }{6 - 7} = \\ = - ( \sqrt{6} - \sqrt{7} ) = \sqrt{7} - \sqrt{6} [/tex]

Ответ: А)