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16)[(3√3+2√7)+(√21+6)]*[(3√3+2√7)-(√21+6)]=(3√3+2√7)²-(√21+6)²=
=27+12√21+28-21-12√21-36=-2
17)(√21 -2) $\sqrt{25+2 \sqrt{84} } =( \sqrt{21} -2)* \sqrt{( \sqrt{21} +2)^2} =( \sqrt{21} -2)( \sqrt{21} +2)$ =21-4=17
18) $\sqrt{( \sqrt{97}+4)(113-8 \sqrt{97}) } \sqrt{( \sqrt{97} +4)( \sqrt{97} -4)}= \sqrt{97-16} = \sqrt{81} =9$
2
1)√5/10;2√3/3;(2√2+√3)/5;
2)2(2-√2)/2=2-√2;4(3+√3)/6=2(3+√3)/3;(∛9+∛3+1)/2;(√15-√6)(√35+√14)/21=
=(7√21-2√210)/21