which is positive definite, and incidentally independent of [tex]x[/tex] and [tex]y[/tex], so [tex]F(x,y)[/tex] attains a minimum [tex]F(-2,2)=-8[/tex].
Meanwhile, we can parameterize the boundary by [tex]\mathbf r(t)=\langle9\cos t,9\sin t\rangle[/tex] with [tex]0\le t\le2\pi[/tex], which gives