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#2
16 มิถุนายน 2013, 19:51
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$\sqrt{20+7\sqrt{10} }=\sqrt{2\sqrt{10}\sqrt{10}+7\sqrt{10} }=\sqrt{\sqrt{10}(2\sqrt{10}+7) }=\sqrt{\sqrt{10}}\sqrt{7+2\sqrt{10} } =\sqrt[4]{10}(\sqrt{5}+\sqrt{2})= \sqrt[4]{10}(\sqrt[4]{25}+\sqrt[4]{4})=\sqrt[4]{250}+\sqrt[4]{40}$
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