Show That the Equation Is Not an Identity by Finding $\cos ( x + \pi ) = \cos x$

question 221

Multiple Choice

Show that the equation is not an identity by finding a value of x for which both sides are defined but not equal.
- $\cos ( x + \pi ) = \cos x$

• A) 0
• B) \(\frac { \pi } { 2 }\)
• C) \(- \frac { \pi } { 2 }\)
• D) \(\frac { 3 \pi } { 2 }\)

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