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Решите задачу:

$\frac{ \sqrt{21}+ \sqrt{7}- \sqrt{3}-1 }{\sqrt{21}+ 2\sqrt{7}- \sqrt{3}-2} = \frac{ \sqrt{7}( \sqrt{3}+ 1)- (\sqrt{3}+1) }{ \sqrt{7} (\sqrt{3}+ 2)- (\sqrt{3}+2)} = \frac{( \sqrt{3}+1)( \sqrt{7}-1) }{( \sqrt{3}+2)( \sqrt{7}-1) } = \frac{\sqrt{3}+1}{\sqrt{3}+2}$
$\frac{\sqrt{3}+1}{\sqrt{3}+2} = \frac{(\sqrt{3}+1)(\sqrt{3}-2)}{(\sqrt{3}+2)(\sqrt{3}-2)} = \frac{3-2 \sqrt{3}+ \sqrt{3}-2 }{3-4} = \frac{1- \sqrt{3} }{-1}= \sqrt{3} -1$