4.
\(-1\le sinx\le1\Rightarrow\sqrt{2}\le\sqrt{sinx+3}\le2\)
\(\Rightarrow\sqrt{2}-1\le y\le1\)
12.
ĐKXĐ: \(sinx+1\ne0\Rightarrow sinx\ne-1\Rightarrow x\ne-\frac{\pi}{2}+k2\pi\)
20.
\(y=tanx\) ko xác định khi \(cosx=0\Leftrightarrow x=\frac{\pi}{2}+k\pi\)
22.
\(y_{min}=y\left(\frac{\pi}{4}\right)=cos\left(\frac{\pi}{4}\right)=\frac{\sqrt{2}}{2}\)