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