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\(âˆĩ x=√7+√6\)
\(∴ \cfrac{1}{x}=\cfrac{1}{√7+√6}\)
\(=\cfrac{(√7-√6)}{(√7+√6)(√7-√6)}\)
\(=\cfrac{√7-√6}{7-6}\)
\(=√7-√6\)

\(∴ x+\cfrac{1}{x}=(√7+√6)+(√7-√6)\)
\(=√7+√6+√7-√6\)
\(=2√7\)

\(x^3+\cfrac{1}{x^3}\) \(=\left(x+\cfrac{1}{x}\right)^3-3.x.\cfrac{1}{x}\left(x+\cfrac{1}{x}\right)\) \(=(2√7)^3-3.2√7\)
\(=56√7-6√7\)
\(=50√7\) [Answer]

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