Given,  $$2x+\ \frac{\ 2}{x}=1$$
    $$2\left(x+\ \frac{\ 1}{x}\right)=1$$
        $$x+\ \frac{\ 1}{x}=\ \frac{\ 1}{2}$$
Therefore, Â $$x^3+\ \frac{\ 1}{x^3}=\ \ \left(x+\ \frac{\ 1}{x}\right)\left(x^2-x.\ \frac{\ 1}{x}+\ \frac{\ 1}{x^2}\right)$$
                   $$=\ \frac{\ 1}{2}\left(x^2+\ \frac{\ 1}{x^2}-1\right)$$
                   $$=\ \frac{\ 1}{2}\left(\left(x+\ \frac{\ 1}{x}\right)^2-2.x.\ \frac{\ 1}{x}-1\right)$$
                  $$=\ \frac{\ 1}{2}\left(\left(\ \frac{\ 1}{2}\right)^2-2-1\right)$$
                  $$=\ \frac{\ 1}{2}\left(\ \frac{\ 1}{4}-3\right)$$
                  $$=\ \frac{\ 1}{2}\left(\ \frac{-11}{4}\right)$$
                  $$=\ \frac{\ -11}{8}$$
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