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c. R=$x^{2}+\frac{2}{x^{3}}=\frac{x^{2}}{3}+\frac{x^{2}}{3}+\frac{x^{2}}{3}+\frac{1}{x^{3}}+\frac{1}{x^{3}}$
$\geq 5.\sqrt[5]{\frac{x^{2}}{3}.\frac{x^{2}}{3}.\frac{x^{2}}{3}.\frac{1}{x^{3}}.\frac{1}{x^{3}}}$
$\Rightarrow A\geq 5.\sqrt[5]{\frac{1}{27}}$
b. $Q=\frac{x^{2}+4x+4}{x}=x+4+\frac{4}{x}\geq 2.\sqrt{x.\frac{4}{x}}+4=8$
