Exercício sobre álgebra elementar

(UNB) Se $\phantom{X}P\,=\,\dfrac{1}{\,\sqrt{\,7\;}\,-\,\sqrt{\,5\;}\;}\phantom{X}$; $\phantom{X}Q\,=\,\dfrac{1}{\,\sqrt{\,8\;}\,-\,\sqrt{\,5\;}\;}\phantom{X}$; $\phantom{X}R\,=\,\dfrac{\,\sqrt{\,5\;}\,+\,\sqrt{\,8\;}\;}{3}\phantom{X}$ então:

P < Q < R

P > Q, Q < R

P > Q > R

P > Q = R

P = Q < R

resposta: (D)
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