Let a,b,ca, b, ca,b,c be positive real numbers such that a1+a+b1+b+c1+c=2.\frac{a}{1 + a} + \frac{b}{1 + b} + \frac{c}{1 + c} = 2.1+aa+1+bb+1+cc=2. Prove that a+b+c2⩾1a+1b+1c.\frac{\sqrt{a} + \sqrt{b} + \sqrt{c}}{2} \geqslant \frac{1}{\sqrt{a}} + \frac{1}{\sqrt{b}} + \frac{1}{\sqrt{c}}.2a+b+c⩾a1+b1+c1.