Demonstrati urmatoarele inegalitati
a) (a+b)/(1+a+b) b)(a+b)/c+(b+c)/a+(c+a)/b≥6,∀a,b,c∈(0;+infinit)
c)1/(a+b)+1/(b+c)+1/(c+a)≤1/2(1/a+1/b+1/c),∀a,b,c∈(0;+infinit)