設ƒ(x) = ax( a > 0 , a ≠ 1 )下列何者正確?
(1)ƒ(x+y)=ƒ(x)ƒ · ƒ(y) (2)ƒ(3)>ƒ(2) (3) (ƒ(x))y=(ƒ(y))x (4)ƒ(x1)+ƒ(x2) / 2>ƒ(x1+x2 / 2) (5)若ƒ(x)+ƒ(-x)=3,則ƒ(2x)+ƒ(-2x)=7