\(A=5-\left(x^2+2\right)^2-\left(y-1\right)^2\le5\)
Amax =5
A=-x2-4x-4-y2+2y-1+5
A=-(x+2)2-(y-1)2+5
A=-((x+2)2+(y-1)2)+5
MaxA=5
Co -x2+4x-y2+2y=-(x2-4x+4)-(y2-2y+1)-5
=-(x-2)2-(y-1)2-5 luon luon lon hon hoac bang -5 voi moi x
dau"=" xay ra khi x=2 va y=1
vay amax=-5khi x=2 va y=1