Let sqrt(x) = y, and the first equation becomes
\(\displaystyle y^{3} - 10y - 3 = 0. \)
This clearly has a solution y = -3, so removing the factor (y + 3), the equation can be written
\(\displaystyle (y+3)(y^{2}-3y-1)=0,\)
yielding two further solutions for y,
\(\displaystyle y = (3 \pm\sqrt{13})/2.\)
That suggests three possible values for sqrt(x), but, (and maybe it's implied by the question ?), surely it is reasonable to assume that sqrt(x) is positive ?
If that's the case, then
\(\displaystyle \sqrt{x}=(3+\sqrt{13})/2.\)
Squaring that,
\(\displaystyle x = (11 + 3\sqrt{13})/2\), so that
\(\displaystyle x + \frac{1}{x}=\frac{11+3\sqrt{13}}{2}+\frac{2}{11+3\sqrt{13}}\),
\(\displaystyle =\frac{(11+3\sqrt{13})^{2}+2^{2}}{2(11+3\sqrt{13})}=\frac{121+33\sqrt{13}}{11+3\sqrt{13}} = 11.\)
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