1.Tìm Min $A=\frac{x^2-2x+2011}{x^2}$
2.a,b,c,d $\epsilon \mathbb{R}$
CMR $a^2+b^2+c^2+d^2\geq a(b+c+d)$
3.Tìm Max $y=-4(x^2-x+1)+3\left | 2x-1 \right |$, với $-1< x< 1$
4 Tìm Max $A=(2x-x^2)(2y-y^2)$ với $0\leq x\leq 2 ,0\leq y\leq \frac{1}{2}$
5. a,b $\epsilon \mathbb{R}$ thỏa mãn a>1, b>1
CMR $\frac{a^3+b^3-(a^2+b^2)}{(a-1)(b-1)}\geq 8$