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For which of the following functions is f(a+b)=f(a)+f(b) for

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Manager
Joined: 13 Dec 2005
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For which of the following functions is f(a+b)=f(a)+f(b) for [#permalink]

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21 Dec 2005, 06:56
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

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^2
B) f(x)=x+1
C) f(x)=square root x (not sure symbol for root)
D) f(x)=2/x
E) f(x)=-3x

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SVP
Joined: 24 Sep 2005
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21 Dec 2005, 07:13
ellisje22 wrote:
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^2
B) f(x)=x+1
C) f(x)=square root x (not sure symbol for root)
D) f(x)=2/x
E) f(x)=-3x

E.
f(a+b)= -3 (a+b)
f(a)+f(b)= -3a + (-3b) = -3(a+b)= f(a+b)

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GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5032

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Location: Singapore

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21 Dec 2005, 07:20
f(a+b) = (a+b)^2 --> out
f(a+b) = a+b+1 --> out
f(a+b) = (a+b)^1/2 --> out
f(a+b) = 2/(a+b) --> out
f(a+b) = -3a-3b --> correct

Ans: E

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Senior Manager
Joined: 05 Oct 2005
Posts: 485

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21 Dec 2005, 10:01
I agree w/ E... by picking numbers

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21 Dec 2005, 10:01
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For which of the following functions is f(a+b)=f(a)+f(b) for

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