f(x) = 1+xln(x+√(1+x^2)) -√(1+x^2)f'(x)= ln(x+√(1+x^2)) + [x/(x+√(1+x^2))] [ 1 + x/√(1+x^2) ] - x/√(1+x^2)=ln(x+√(1+x^2)) + x/√(1+x^2) - x/√(1+x^2)=ln(x+√(1+x^2))> ln1=0min f(x) = f(0) = 1-1 =0f(x) >01+xln(x+√(1+x^2)) > √(1+x^2)