Gaokao Math Practice Question
11. (5 分) 已知角 $\alpha$ 的顶点为坐标原点, 始边与 $\mathrm{x}$ 轴的非负半轴重合, 终边上 有两点 $A(1, a), B(2, b)$, 且 $\cos 2 \alpha=\frac{2}{3}$, 则 $|a-b|=(\quad)$
- A.$\frac{1}{5}$
- B.$\frac{\sqrt{5}}{5}$
- C.$\frac{2 \sqrt{5}}{5}$
- D.1
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