1) Do $-1\le\sin x\le 1$ $\forall x$
$\Rightarrow 1\ge-\sin x\ge-1$
$\Rightarrow 1+5\ge-\sin x+5\ge-1+5$
$\Rightarrow 6\ge-\sin x+5\ge4$
$\Rightarrow $ GTLN $y=6$ khi $\sin x=-1$
GTNN $y=4$ khi $\sin x=1$
2) Do $-1\le \cos x\le1$ $\forall x$
$\Rightarrow -3\le 3\cos x\le 3$
$\Rightarrow -3-2\le\cos x-2\le3-2$
$\Rightarrow -5\le\cos x-2\le 1$
$\Rightarrow $ GTLN $y=1$ khi $\cos x=1$
GTNN $y=-5$ khi $\cos x=-1$
3) Do $-1\le\sin (x-\dfrac{\pi}{3})\le 1$ $\forall x$
$\Rightarrow -2\le\sin (x-\dfrac{\pi}{3})\le 2$
$\Rightarrow -2+3\le\sin (x-\dfrac{\pi}{3})+3\le 2+3$
$\Rightarrow 1\le\sin (x-\dfrac{\pi}{3})+3\le 5$
$\Rightarrow $ GTLN $y=5$ khi $\sin (x-\dfrac{\pi}{3})=1$
GTNN $y=1$ khi $\sin (x-\dfrac{\pi}{3})=-1$
Các câu tiếp tương tự, bạn làm nhé, dài quá.
