1) Cho $x+y\geq 1;x>0$ Tìm Min $D=\frac{8x^{2}+y}{4x}+y^{2}$
2) Cho a,b>0 $\frac{1}{a}+\frac{1}{b}=2$ Tìm Max $Q=\frac{1}{a^{4}+b^{2}+2ab^{2}}+\frac{1}{a^{2}+b^{4}+2a^{2}b}$
3) Cho x,y>0 $x\geq 2y$ Tìm Min $M=\frac{x^{2}+y^{2}}{xy}$
4) Cho $a,b,c\geq 0;a+b+c=3$ Chứng minh: $(a-1)^{3}+(b-1)^{3}+(c-1)^{3}\geq \frac{-3}{4}$