Gaokao Math Practice Question
2. （5 分) 平面向量 $\vec{a}, \vec{b}$, 已知 $\vec{a}=(4,3), 2 \vec{a}+\vec{b}=， 3,18 ＼mathrm{~, ~ 则 ~} \vec{a}, \vec{b}$ 夹角 的余弦值等于 ( $)$
- A.$\frac{8}{65}$
- B.$-\frac{8}{65}$
- C.$\frac{16}{65}$
- D.$-\frac{16}{65}$
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