Find the Exact Value by Using a Half-Angle Identity $\cos \frac { x } { 2 }$

question 241

Multiple Choice

Find the exact value by using a half-angle identity.
-Find $\cos \frac { x } { 2 }$ , given that $\sec x = 4$ and $x$ terminates in $0 < x < \frac { \pi } { 2 }$ .

• A) \(\frac { \sqrt { 6 } } { 4 }\)
• B) \(\frac { \sqrt { 8 + 2 \sqrt { 15 } } } { 4 }\)
• C) \(\frac { \sqrt { 10 } } { 4 }\)
• D) \(\frac { \sqrt { 8 - 2 \sqrt { 15 } } } { 4 }\)

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