Gaokao Math Practice Question
10. (5 分) 若 $\cos \alpha=-\frac{4}{5}, \alpha$ 是第三象限的角, 则 $\sin \left(\alpha+\frac{\pi}{4}\right)=(\quad)$
- A.$-\frac{7 \sqrt{2}}{10}$
- B.$\frac{7 \sqrt{2}}{10}$
- C.$\frac{\sqrt{2}}{10}$
- D.$\frac{\sqrt{2}}{10}$
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