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Có : BT= lim_{x \to 0}\frac{[\sqrt[3]{1+3x}-(1+x)]+[x(1-\sqrt{1-x})]}{x^3+x^2} =lim_{x \to 0}\frac{\frac{-x^3-3x^2}{\sqrt[3]{(1+3x)^2}+\sqrt[3]{1+3x}(1+x)+(1+x)^2}+\frac{x^2}{1+\sqrt{1-x}}}{x^3+x^2} =lim_{x \to 0 }\frac{\frac{-x-3}{MS}+\frac{1}{1+\sqrt{1-x}}}{x+1}=\frac{-1}{2}
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