F(x)=x+ c/x ≥ 2 radical sign (x * c/x)≥2 radical sign c

And because f(x)≥f(2)

f(2)=2+2/c

So 2+2/c=2 C.

Multiply both sides by two.

4-4 root number c+c=0

The square of (radical c-2) =0

Root number c =2

c=4

Because f(x)≥f(2)

So 0≤c≤4