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$\dfrac{-\dfrac 1 2}{x}=-\dfrac 7 3 \\ -\dfrac 1 2 = -\dfrac 7 3 x \\ \dfrac 1 2 = \dfrac 7 3 x \\ \dfrac 1 2 \times \dfrac 3 7 = x \\ x = \dfrac {3}{14}$