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$\sqrt{( \frac{55}{7} )^{2} -(6 \frac{2}{7})^{2} } - \frac{5}{7} = \\ = \sqrt{( \frac{55}{7} )^{2}-( \frac{44}{7})^{2} }- \frac{5}{7} = \\ = \sqrt{( \frac{55}{7}- \frac{44}{7})( \frac{55}{7}+ \frac{44}{7}) }- \frac{5}{7} = \\ = \sqrt{ \frac{11}{7}* \frac{99}{7} } - \frac{5}{7} = \\ = \sqrt{ \frac{1089}{49} } -\frac{5}{7} = \\ = \frac{33}{7} -\frac{5}{7} =\frac{28}{7} =4$
Ответ: 4