Use a double-angle formula to find the exact value of $\cos 2 u$ when $\sin u = \frac { 5 } { 13 }$, where $\frac { \pi } { 2 }

Question

Use a double-angle formula to find the exact value of $\cos 2 u$ when $\sin u = \frac { 5 } { 13 }$, where $\frac { \pi } { 2 } < u < \pi$.
A) $\cos 2 u = - \frac { 94 } { 169 }$
B) $\quad \cos 2 u = \frac { 60 } { 169 }$
C) $\cos 2 u = \frac { 120 } { 169 }$
D) $\cos 2 u = \frac { 119 } { 169 }$
E) $\cos 2 u = - \frac { 288 } { 169 }$

Quizplus · Accepted Answer

The Answer of Use a double-angle formula to find the exact value of $\cos 2 u$ when $\sin u = \frac { 5 } { 13 }$, where $\frac { \pi } { 2 } < u < \pi$.
A) $\cos 2 u = - \frac { 94 } { 169 }$
B) $\quad \cos 2 u = \frac { 60 } { 169 }$
C) $\cos 2 u = \frac { 120 } { 169 }$
D) $\cos 2 u = \frac { 119 } { 169 }$
E) $\cos 2 u = - \frac { 288 } { 169 }$

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