A=\(2x^2+5x+2\) 

  =\(2\left(x^2+\dfrac{5}{2}x+1\right)\) 

  =\(2\left[\left(x^2+\dfrac{5}{2}x+\dfrac{25}{16}\right)-\dfrac{25}{16}+1\right]\) 

  =\(2\left(x+\dfrac{5}{4}\right)^2-\dfrac{9}{8}\ge-\dfrac{9}{8}\)  

A\(\min\limits\) =\(-\dfrac{9}{8}\)  khi x=\(-\dfrac{5}{4}\)

A=\(x^2+4x+4\)

  =\(\left(x+2\right)^2\le0\)

De A\(\max\limits\) =0 thi x=-2

sai roi ban phai la \(\le\) moi dung