Consider the derivation of an alternate form of the cosine double angle identity.
1. \( \cos ( 2 x ) = \cos ^ { 2 } ( x ) - \sin ^ { 2 } ( x ) \)
2. \(= \cos ^ { 2 } ( x ) - ( 1 - \cos ^ { 2 } ( x ) ) \)
3. \(= \cos ^ { 2 } ( x ) - 1 - \cos ^ { 2 } ( x ) \)
4. \(= 2 \cos ^ { 2 } ( x ) - 1\)
What is the error in this derivation?
In step \( 1 , \cos ( 2 x ) \) is equal to \( \cos ^ { 2 } ( x ) + \sin ^ { 2 } ( x ) \) .
In step \( 2 , \sin ^ { 2 } ( x ) \) should have been replaced with \( 1 + \) \( \cos ^ { 2 } ( x ) \) .
In step \( 3 , \cos ^ { 2 } ( x ) - 1 - \cos ^ { 2 } ( x ) \) should be \( \cos ^ { 2 } ( x ) - 1 \) \( + \cos ^ { 2 } ( x ) \)
In \( \operatorname { step } 4 , 2 \cos ^ { 2 } ( x ) - 1 \) should be \( 1 - 2 \cos ^ { 2 } ( x ) \)