Toán Lớp 9: Rút gọn:
$\frac{8}{1–\sqrt[]{5}}$ $+$ $\frac{5 – 2\sqrt[]{5}}{\sqrt[]{5} – 2}$ $–$ $\frac{1}{2}$$\sqrt[]{80}$
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Toán Lớp 9: Rút gọn:
$\frac{8}{1–\sqrt[]{5}}$ $+$ $\frac{5 – 2\sqrt[]{5}}{\sqrt[]{5} – 2}$ $–$ $\frac{1}{2}$$\sqrt[]{80}$
Comments ( 1 )
\dfrac{8}{{1 – \sqrt 5 }} + \dfrac{{5 – 2\sqrt 5 }}{{\sqrt 5 – 2}} – \dfrac{1}{2}\sqrt {80} \\
= \dfrac{{8\left( {1 + \sqrt 5 } \right)}}{{1 – 5}} + \dfrac{{\sqrt 5 \left( {\sqrt 5 – 2} \right)}}{{\sqrt 5 – 2}} – \dfrac{1}{2}.4\sqrt 5 \\
= \dfrac{{8\left( {1 + \sqrt 5 } \right)}}{{ – 4}} + \sqrt 5 – 2\sqrt 5 \\
= – 2\left( {1 + \sqrt 5 } \right) – \sqrt 5 \\
= – 2 – 2\sqrt 5 – \sqrt 5 \\
= – 2 – 3\sqrt 5
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