Phương trình $2\cos x + \sqrt 2 = 0$ có tất các nghiệm là
![](https://m.moon.vn/Images/Teachers/nguyenoanh8892/To%C3%A1n/04/1/7.png)
A.
![](https://m.moon.vn/Images/Teachers/nguyenoanh8892/To%C3%A1n/04/1/7a.png)
B.
![](https://m.moon.vn/Images/Teachers/nguyenoanh8892/To%C3%A1n/04/1/7b.png)
C.
![](https://m.moon.vn/Images/Teachers/nguyenoanh8892/To%C3%A1n/04/1/7c.png)
D.
![](https://m.moon.vn/Images/Teachers/nguyenoanh8892/To%C3%A1n/04/1/7d.png)
Đáp án C
![](https://m.moon.vn/Images/Teachers/nguyenoanh8892/To%C3%A1n/04/1/7e.png)