Find the Exact Value by Using a Half-Angle Identity $\cos 22.5 ^ { \circ }$

question 4

Multiple Choice

Find the exact value by using a half-angle identity.
- $\cos 22.5 ^ { \circ }$

• A) \(\frac { 1 } { 2 } \sqrt { 2 - \sqrt { 2 } }\)
• B) \(- \frac { 1 } { 2 } \sqrt { 2 + \sqrt { 2 } }\)
• C) \(\frac { 1 } { 2 } \sqrt { 2 + \sqrt { 2 } }\)
• D) \(- \frac { 1 } { 2 } \sqrt { 2 - \sqrt { 2 } }\)

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