bai tren lam (sai co ban) dung de ≠ ko phai de nay.
copy nen xem de dung chua.

Sai thì sửa

b)
B=xy/(x^2+2y^2)
dk. xy+4≤2y
x^2+2y^2>0 tim gt ln B=> xet x.y>0( x,y cung dau)
B=1/(x/y+2y/x)
dk.xy+4≤2y=y(x-2)≤-4

x/y≤2/y-4/y^2=1/4-(2/y-1/2)^2
x/y=t=>0<t≤1/4
B=1/(t+2/t)
t+2/t≥1/4+2/(1/4)=33/4
B≤4/33
khi t=1/4
x=y/4
y^2/4 -2y+4≤0
(y/2-2)^2≤0
(x,y)=(1,4)

@onmath (ok ban)
ban sua van chua dung

dk bai toan
xy+4≤2y (hinh nhu ban ko dung)
thu lai cho ban thay cai sai (co ban)
x=√2y
<=>√2.y^2-2y+4≤0
=>y=¿