x2-2+\(\frac{1}{x^2}\) +x2-xy+\(\frac{y^2}{4}=2-xy\)
=>\(\left(x-\frac{1}{x}\right)^2+\left(x-\frac{y}{2}\right)^2=2-xy\)
Do VT\(\ge0\)=> 2-xy\(\ge0\)
=>xy\(\le2\)
Vậy Maxxy=2 (dấu bằng tự làm)
à mình đọc nhầm tưởng là gtln.
\(x^2-2+\frac{1}{x^2}+x^2\)\(+xy+\frac{y^2}{4}=2+xy\)
=>\(\left(x-\frac{1}{x}\right)^2+\left(x+\frac{y}{2}\right)^2\)=2+xy
Do VT\(\ge0\)=> 2+xy\(\ge0\)
=>xy\(\ge-2\)
Vậy Minxy=2