Acertain function f has the property that f(x+y)=
f(x)+f(y) for all values of x and y. which of the
following statements must be true when a=b?
i. f(a+b)=2f(a).
ii. f(a+b)=[f(a] to the power of 2.
iii. f(b) +f(b)=f(2a)

The problem ask to choose among the following statement that tells the truth about the said function f and the best answer among the following statement is in statement I. f(a+b)=2f(a) and statement III. f(b)+f(b) = f(2a). I hope you are satisfied with my answer and feel free to ask for more 

Ibelieve it is