[計量] 請教pp1 ps 63

[yuanyen100 (2009 is a big year!!)]

63.For which of the following function is f(a+b) = f(a)+f(b) for all positive
numbers a and b?

(A) f(x)=x 2
(B) f(x)=x+1
(C)
(D)
(E) f(x)=-3x

ans:E

之前已經有人討論  但是還是不懂題目在講什麼

可否幫忙解惑  感激不盡

Orz

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