(\sqrt{6+2\sqrt5}+\sqrt{6-2\sqrt5})^2=20
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(\sqrt{6+2\sqrt5}+\sqrt{6-2\sqrt5})^2=
(\sqrt{6+2\sqrt5})^2+2\sqrt{(6+2\sqrt5)(6-2\sqrt5)}+(\sqrt{6-2\sqrt2})^2=
6+2\sqrt2+2(6^2-4*5)+6-2\sqrt2=6+2*\sqrt{36-20}+6=
6+2*\sqrt{16}+6=6+2*4+6=20
zastosowany wzór
(a+b)(a-b)=a^2-b^2