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by kshin78 » Sat Aug 02, 2008 1:17 pm
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. f(x) = sqr of x

d. f(x) = 2/x

e. f(x) = -3x


Thanks!!!

I don't have the slightest idea what the question is even asking for..
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by pepeprepa » Sat Aug 02, 2008 2:54 pm
You look for a function which makes: f(a+b) = f(a) + f(b)
Start from E to A in this kind of question, you will find the answer faster in general.

So with E) the function is f(x)=-3x
f(a)=-3a
f(b)=-3b
f(a+b)=-3(a+b)=-3a-3b

You clearly have f(a+b) = f(a) + f(b) so the right answer is E.
Try to reimplace with a and b for A,B,C,D: you will not get f(a+b) = f(a) + f(b)
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