For which of the following functions is f(a+b)= f(a) + f(b) for all positive numbers a and b?
a. f(x) = x*x
b. f(x) = x + 1
c. f(x) = sq. root of x
d. f(x) = 2/x
e. f(x) = -3x
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We can find the answer by replacing the value of x by a, b & (a+b)
a. (a+b)*(a+b) != a*a + b*b
b. a + b + 1 != a + 1 + b + 1
c. sqrt(a+b) != sqrt(a) + sqrt(b)
d. 2/(a+b) != 2/a + 2/b
e. -3(a+b) = -3a - 3b (TRUE)
Hence the answer is option E
