Use a Double-Angle Formula to Find the Exact Value Of \cos

question 69

Multiple Choice

Use a double-angle formula to find the exact value of $\cos 2 u$ when $\sin u = \frac { 8 } { 17 }$ , where $\frac { \pi } { 2 } < u < \pi$ .

• A) \(\cos 2 u = - \frac { 97 } { 289 }\)
• B) \(\quad \cos 2 u = \frac { 120 } { 289 }\)
• C) \(\quad \cos 2 u = \frac { 240 } { 289 }\)
• D) \(\cos 2 u = \frac { 161 } { 289 }\)
• E) \(\cos 2 u = - \frac { 450 } { 289 }\)

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