\(y=2\left(\frac{1}{2}sinx+\frac{\sqrt{3}}{2}cosx\right)=2sin\left(x+\frac{\pi}{3}\right)\)
Do \(-1\le sin\left(x+\frac{\pi}{3}\right)\le1\Rightarrow-2\le y\le2\)
\(y_{min}=-2\) khi \(sin\left(x+\frac{\pi}{3}\right)=-1\)
\(y_{max}=2\) khi \(sin\left(x+\frac{\pi}{3}\right)=1\)