a)Ta có \(\left(2x+1\right)^2\ge0,y^2\ge0\) => \(P=\left(2x+1\right)^2+y^2-3\ge-3\)
Dấu = xảy ra <=> \(x=-\dfrac{1}{2},y=0\)
b)Ta có \(-\left(x+\dfrac{1}{2}\right)^2\le0,-\left(2x+y\right)^2\le0\) => \(Q=-\left(x+\dfrac{1}{2}\right)^2-\left(2x+y\right)^2+10\le10\)
Dấu = xảy ra <=> \(x=-\dfrac{1}{2},y=-2x=1\)