1. Cho x,y >0 :
x+y+xy=3
Tìm min, max:
P= x2 + y2 - $\frac{3x}{y+1}$ - $\frac{3y}{x+1}$ - $\frac{xy}{x+y}$
2. Cho x,y : $\sqrt{x+1} + \sqrt{y+1}=4$
Tìm max, min của: P= xy + $\frac{64}{4-x-y}$
3. Cho 0<x,y $\leq$ 1 :
x+y=4xy
Tìm min, max: M= x2 +y2 -4xy