Because f(x)≥x and f(2)≥2.

Because x∈( 1, 3), f(x)≤ 1/8(x+2)? So f(2)≤2

Taken together, we can get two: f(2)=2.

The second question:

4a+2b+c=2 from f(2)=2.

4a-2b+c=0 from f(-2)=0.

Solution: b= 1/2 c= 1-4a.

f(x)=ax？ +x/2+ 1-4a≥x applies to all real numbers.

Is that an axe? -x/2+ 1-4a≥0 holds for all real numbers.

So the discriminant = 1/4-4a( 1-4a)≤0.

Get (4a- 1/2)？ ≤0

So a =1/8c =1-4a =1/2.

f(x)=x？ /8+x/2+ 1/2

Is it more detailed?