Giải giúp e vs ạ $f(x)=\sin x+\cos x$ 
Có thể ns cách làm chi tiết k ạ
$\sin x+\cos x=\sqrt{2}\sin (x+\frac{\pi}{4})$
ta có: $-1\leq \sin (x+\frac{\pi}{4})\leq 1\Leftrightarrow -\sqrt{2}\leq \sqrt{2}\sin (x+\frac{\pi}{4})\leq \sqrt{2}$
ngoài cách này thì có thể xét hàm số trong khoảng $[0;2\pi]$ tìm nghiệm rồi so sánh $f(0), f(2\pi), f(x1),f(x2),....$

Bạn cần đăng nhập để có thể gửi đáp án

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