Exercício sobre geometria analítica

(MACKENZIE) Considere a figura abaixo. O comprimento do segmento $\phantom{X}\overline{MN} \phantom{X}$ é:

$\,\sqrt{2\;}\,-\,{\dfrac{\;1\;}{2}}\,$

$\,\sqrt{2\;}\,+\,{\dfrac{\;1\;}{\sqrt{2\;}}}\,$

$\,\sqrt{2\;}\,+\,1\phantom{\dfrac{X}{X}}\,$

$\,1\,-\,{\dfrac{\;\sqrt{\;2\;}\;}{2}}\,$

$\,\sqrt{2\;}\,-\,1\,$

resposta: (E)
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