There is something wrong with this question, so there is no unique answer. Maybe you typed the question wrong.

Because it is impossible to get the exact value of f (odd number) when converting f(x).

This question should be limited. For example, f(x) is odd function.

The following solutions can be obtained:

F(x) is odd function.

So f(x)=-f(-x)

f(-2)=-f(2)=- 1

f( 1)= f(- 1+2)= f(- 1)+f(2)= f(- 1)+ 1

And f( 1)=-f(- 1).

f( 1)=0.5。

f(5)= f(3+2)= f(3)+f(2)= f( 1+2)+f(2)= f( 1)+2f(2)= 0.5+2 * 1

=2.5