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[latex]\Big (1- \frac{c+\sqrt{c}}{c-1} \Big ): \frac{2}{\sqrt{c}-1} =\Big (1- \frac{\sqrt{c}(\sqrt{c}+1)}{(\sqrt{c}-1)(\sqrt{c}+1)} \Big )\cdot \frac{\sqrt{c}-1}{2} =\\\\=\Big (1-\frac{\sqrt{c}}{\sqrt{c}-1}\Big )\cdot \frac{\sqrt{c}-1}{2} = \frac{\sqrt{c}-1-\sqrt{c}}{\sqrt{c}-1} \cdot \frac{\sqrt{c}-1}{2} = \\\\=\frac{-1}{\sqrt{c}-1} \cdot \frac{\sqrt{c}-1}{2}=-\frac{1}{2} [/latex]