СРОЧНО ПЛИЗ 63 номер!!!!!!!

Решите задачу:

$\sqrt{21-12 \sqrt{3} } + \sqrt{21+12 \sqrt{3} } = \sqrt{(\sqrt{21-12 \sqrt{3} } + \sqrt{21+12 \sqrt{3} }~~) ^2} = \\= \sqrt{21-12 \sqrt{3} +2\sqrt{21-12 \sqrt{3} }*\sqrt{21+12 \sqrt{3} }+21+12 \sqrt{3} } = \\= \sqrt{21+21-12 \sqrt{3} +12 \sqrt{3}+2\sqrt{(21-12 \sqrt{3})(21+12 \sqrt{3}) }}= \\ = \sqrt{42+2 \sqrt{441-144*3} } =\sqrt{42+2 \sqrt{441-432} } =\sqrt{42+2 \sqrt{9} } = \\ = \sqrt{42+2*3} = \sqrt{42+6} = \sqrt{48}$