Use a Double-Angle Formula or a Half-Angle Formula to Simplify $\cos ^ { 2 } 2 \theta - \sin ^ { 2 } 2 \theta$

question 1

Essay

Use a double-angle formula or a half-angle formula to simplify $\cos ^ { 2 } 2 \theta - \sin ^ { 2 } 2 \theta$ .

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