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