Номер 4, пожалуйста помогите!

$\frac{5-2 \sqrt{6} }{ \sqrt{5}+ \sqrt{2} } - \frac{ \sqrt{5}- \sqrt{2} }{15+6 \sqrt{6} } = \frac{(5-2 \sqrt{6})( \sqrt{5}- \sqrt{2} ) }{( \sqrt{5}+ \sqrt{2})( \sqrt{5}- \sqrt{2}) }- \frac{( \sqrt{5}- \sqrt{2})(15-6 \sqrt{6} ) }{(15+6 \sqrt{6})(15-6 \sqrt{6}) }= \\ \frac{5 \sqrt{5}-5 \sqrt{2}-2 \sqrt{5} \sqrt{6}+2 \sqrt{2} }{5-2}- \frac{15 \sqrt{5}-6 \sqrt{5} \sqrt{6}-15 \sqrt{2}+6 \sqrt{6} \sqrt{2} }{225-216} = \\ \frac{ \sqrt{5}(5-2 \sqrt{6})- \sqrt{2}(5-2 \sqrt{6}) }{3} -$ $\frac{15( \sqrt{5}- \sqrt{2})-6 \sqrt{6}( \sqrt{5}- \sqrt{2})}{9}= \frac{( \sqrt{5}- \sqrt{2})(5-2 \sqrt{6}) }{3}- \frac{3(5-2 \sqrt{6})( \sqrt{5}- \sqrt{2}) }{9}=0$ - верно