(A) : f(a)=a^2 , f(b)=b^2
f(a+b)=(a+b)^2which is not equal to (a^2) + (b^2) [ f(a) + f(b) ]
(B): f(a)=a+1 , f(b)=b+1 , f(a+b)=a+b+1 which is not equal to (a+1)+(b+1) = a+b+2 [ f(a) + f(b) ]
(C): f(a)= √a , f(b)= √b , f(a+b) = √((a+b) which is not equal to √a+√a [ f(a) + f(b) ]
(D) : f(a)=2/3 , f(b) = 2/3 , f(a+b)=2/3 which is not equal to 2/3 + 2/3 [ f(a) + f(b) ]
(E): f(a)= -3a , f(b)= -3b , f(a+b)= -3(a+b)=(-3a) + (-3b)=f(a) + f(b)
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