V
vingotomai_gl


cho a,b,c >0 và [TEX]a^2 + b^2 +c^2\leq4[/TEX]
CMR [TEX]\frac{ab +1}{(a+b)^2}+\frac{bc+1}{(b+c)^2}+\frac{ca+1}{(c+a)^2}\geq3[/TEX]
CMR [TEX]\frac{ab +1}{(a+b)^2}+\frac{bc+1}{(b+c)^2}+\frac{ca+1}{(c+a)^2}\geq3[/TEX]