(1 + cos 2x)/1- cos 2x)
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$\dfrac{1+\cos(2x)}{1-\cos(2x)} = \dfrac{1+\cos(2x)}{2} \cdot \dfrac{2}{1-\cos(2x)} = \dfrac{\cos^2{x}}{\sin^2{x}} = \cot^2{x}$
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