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- $ f\\\left( x \\\right) = {x^2} + \\\frac{1}{2}\\\cos 2x$.
- $ f\\\left( x \\\right) = {x^2} - \\\frac{1}{2}\\\cos 2x$.
- $ f\\\left( x \\\right) = 2 + 2\\\cos 2x$.
- $ f\\\left( x \\\right) = 2 - 2\\\cos 2x$.