\(y=\dfrac{2+sin^2x}{4}\)
Có \(0\le sin^2x\le1\)
\(\Leftrightarrow2\le sin^2x+2\le3\)
\(\Leftrightarrow\dfrac{1}{2}\le y\le\dfrac{3}{2}\)
\(\Rightarrow miny=\dfrac{1}{2}\) khi \(sinx=0\Leftrightarrow x=k\pi\)
\(\Rightarrow maxy=\dfrac{3}{2}\) khi \(sin^2x=1\Leftrightarrow cosx=0\Leftrightarrow x=\dfrac{\pi}{2}+k\pi\)