[tex]\fn_cm \frac{\left ( 5+2\sqrt{6} \right ).\left ( 49-20\sqrt{6} \right ).\sqrt{5-2\sqrt{6}}}{9\sqrt{3}-11\sqrt{2}}[/tex]
Chứng minh là số nguyên tố
$\dfrac{\left ( 5+2\sqrt{6} \right ).\left ( 49-20\sqrt{6} \right ).\sqrt{5-2\sqrt{6}}}{9\sqrt{3}-11\sqrt{2}}
\\=\dfrac{\sqrt{5+2\sqrt{6}}.(49-20\sqrt{6}).\sqrt{(5+2\sqrt{6})(5-2\sqrt{6})}}{9\sqrt{3}-11\sqrt{2}}
\\=\dfrac{\sqrt{5+2\sqrt{6}}.(49-20\sqrt{6}).\sqrt{25-24}}{9\sqrt{3}-11\sqrt{2}}
\\=\dfrac{\sqrt{(\sqrt{3}+\sqrt{2})^2}.(49-20\sqrt{6})}{9}
\\=\dfrac{(\sqrt{3}+\sqrt{2})(49-20\sqrt{6})}{9\sqrt{3}-11\sqrt{2}}
\\=\dfrac{49\sqrt{3}-60\sqrt2+49\sqrt2-40\sqrt3}{9\sqrt{3}-11\sqrt{2}}
\\=\dfrac{9\sqrt3-11\sqrt2}{9\sqrt{3}-11\sqrt{2}}=1$
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