câu B
\(B=2\left(x+3\right)^2-3\left(x+2\right)^2=2\left[\left(x+3\right)^2-\left(x+2\right)^2\right]-\left(x+2\right)^2\)\(B=2\left[\left(x+3-x-2\right)\left(x+3+x+2\right)\right]-\left(x+2\right)^2=2\left(2x+5\right)-\left(x^2+4x+4\right)\)\(B=4x+10-\left(x^2+4x+4\right)=6-x^2\le6\)
GTLN B =6 tại x =0
không có GTNN