25 tháng 12 2023 lúc 20:03
\(B=\dfrac{1}{\sqrt{3}-2}-\dfrac{1}{\sqrt{3}+2}\)
\(=\dfrac{\sqrt{3}+2-\left(\sqrt{3}-2\right)}{\left(\sqrt{3}-2\right)\left(\sqrt{3}+2\right)}\)
\(=\dfrac{\sqrt{3}+2-\sqrt{3}+2}{3-4}=\dfrac{4}{-1}=-4\)
\(C=\sqrt{8-2\sqrt{15}}-\sqrt{5}\)
\(=\sqrt{5-2\cdot\sqrt{5}\cdot\sqrt{3}+3}-\sqrt{5}\)
\(=\sqrt{\left(\sqrt{5}-\sqrt{3}\right)^2}-\sqrt{5}\)
\(=\sqrt{5}-\sqrt{3}-\sqrt{5}=-\sqrt{3}\)
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