BDT <=>a^2/3+(b+c)^2-3bc-a(b+c)>0
<=>a^2/4+(b+c)^2-a(b+c)+a^2/12-3bc>0
<=>(a/2-b-c)^2+a^2/12-3/a>0
<=>(a/2-b-c)^2+(a^3-36)/12a>0
ta co (a/2-b-c)>0
a^3-36>0
a>0
=> dpcm
TQ
<=>a^2/4+(b+c)^2-a(b+c)+a^2/12-3bc>0
<=>(a/2-b-c)^2+a^2/12-3/a>0
<=>(a/2-b-c)^2+(a^3-36)/12a>0
ta co (a/2-b-c)>0
a^3-36>0
a>0
=> dpcm
TQ