Use the Half-Angle Formulas to Determine the Exact Value of the Following

question 23

Multiple Choice

Use the half-angle formulas to determine the exact value of the following.
$$\cos \left( - 22.5 ^ { \circ } \right)$$

• A) \(- \frac { \sqrt { 2 + \sqrt { 2 } } } { 2 }\)
• B) \(\frac { \sqrt { 2 - \sqrt { 3 } } } { 2 }\)
• C) \(- \frac { \sqrt { 2 - \sqrt { 3 } } } { 2 }\)
• D) \(\frac { \sqrt { 3 - \sqrt { 2 } } } { 2 }\)
• E) \(\frac { \sqrt { 2 + \sqrt { 3 } } } { 2 }\)

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