Prove the Identity $$\cos 4 x + \cos 2 x = 2 - 2 \sin ^ { 2 } 2 x - 2 \sin ^ { 2 } x$$

question 114

Essay

Prove the identity.
- $$\cos 4 x + \cos 2 x = 2 - 2 \sin ^ { 2 } 2 x - 2 \sin ^ { 2 } x$$

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