Toán Lớp 9: rút gọn $\sqrt[3]{9+4\sqrt{5}}$
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Toán Lớp 9: rút gọn $\sqrt[3]{9+4\sqrt{5}}$
Comments ( 1 )
$\sqrt[3]{9+4\sqrt{5}}$
=$\sqrt[3]{(\frac{3}{2})³+3.\frac{9}{4}.\frac{\sqrt[]{5}}{2}+3.\frac{3}{2}\frac{5}{4}+(\frac{\sqrt[]{5}}{2})³}$
=$\sqrt[3]{(\frac{3+\sqrt[]{5}}{2})³}$
=(3+sqrt5)/2