4. (5 分) 已知向量 $\vec{a}, \vec{b}$ 满足 $|\vec{a}|=1, \vec{a} \cdot \vec{b}=-1$, 则 $\vec{a} \bullet(2 \vec{a}-\vec{b})=(\quad ）$
Gaokao · Math · previous-year question
- A.4
- B.3
- C.2
- D.0
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