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Решите задачу:

$\frac{20}{7- \sqrt{29} } - \frac{15}{6+ \sqrt{21} } - \frac{8}{ \sqrt{29}- \sqrt{21} } =\\ \frac{20(7+ \sqrt{29})}{(7- \sqrt{29})(7+\sqrt{29}) } - \frac{15(6- \sqrt{21})}{(6+ \sqrt{21})(6- \sqrt{21}) } - \frac{8(\sqrt{29}+ \sqrt{21})}{( \sqrt{29}- \sqrt{21})(\sqrt{29}+ \sqrt{21}) } =\\ \frac{20(7+ \sqrt{29})}{49-29 }- \frac{15(6- \sqrt{21})}{36-21 }-\frac{8(\sqrt{29}+ \sqrt{21})}{29-21}=\\ 7+ \sqrt{29} -6+ \sqrt{21} - \sqrt{29}- \sqrt{21} =1$