chung minh rang 19x2+54y2+16z2−16xz+36xy−24yz≥0
2,cho 6 so thoa man mx2+2nx+p≥0,ax2+bx+c≥0 chung minh rng max2+2nbx+pc≥0
vs moi x
cho x,y,z>0 dat a=√x2+y2+xy√3
b= √x2+z2+xz√3
c=√y2+z2−x2
cmr:c2+ab<a2+b2 va |xy+xz+yz√3|2=|(a+b)2−c2|.|c2−(a−b)2|