Gaokao Math Practice Question
10. (5 分) 已知锐角 $\triangle A B C$ 的内角 $A, B, C$ 的对边分别为 $a, b, c, 23 \cos ^{2} A+\cos 2 A=0$ , $a=7, c=6$, 则 $b=(\quad)$
- A.10
- B.9
- C.8
- D.5
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