Algebra question

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ornelaspedro: Junior | Next Rank: 30 Posts; Posts: 10; Joined: Wed Feb 18, 2009 9:15 pm

by ornelaspedro » Thu Apr 30, 2009 3:38 pm

For which of the following functions is f(a+b) = f(a) + f(b) for all positive numbers a and b?

The answer is -3x. Could anybody show me how to get to the answer.

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Source: Beat The GMAT — Problem Solving | Thu Apr 30, 2009 3:38 pm

dumb.doofus: Master | Next Rank: 500 Posts; Posts: 435; Joined: Sat Sep 27, 2008 2:02 pmFollowed by: 1 member; Location: San Jose, CA; Thanked: 43 times; GMAT Score:720

Re: Algebra question

by dumb.doofus » Thu Apr 30, 2009 3:49 pm

ornelaspedro wrote:For which of the following functions is f(a+b) = f(a) + f(b) for all positive numbers a and b?

The answer is -3x. Could anybody show me how to get to the answer.

Bouncer.. didnt get it.. dont you need to define what is F(x) .. what is given is just one property of F(x)..

I feel something is missing here..

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ornelaspedro: Junior | Next Rank: 30 Posts; Posts: 10; Joined: Wed Feb 18, 2009 9:15 pm

Post subject: Re: Algebra question

by ornelaspedro » Thu Apr 30, 2009 3:59 pm

I know !!! It makes no sense to me either. I got this question on the gmatprep practice test one. That's all the information you are given. Anyways, if you can think of something I would really appreciate it.

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dumb.doofus: Master | Next Rank: 500 Posts; Posts: 435; Joined: Sat Sep 27, 2008 2:02 pmFollowed by: 1 member; Location: San Jose, CA; Thanked: 43 times; GMAT Score:720

by dumb.doofus » Thu Apr 30, 2009 9:25 pm

aaaaaaaaaaaah.... got it..

it's pretty simple.. if I am thinking correctly

well, just put the values..

let's say f(x) = -3x

so f(a+b) = -3(a+b) = -3a -3b --- (1)

and f(a) + f(b) = -3a - 3b --- (2)

(1) = (2)

so f(x) = -3x suffices f(a+b) = f(a) + f(b)

HTH

One love, one blood, one life. You got to do what you should.
https://dreambigdreamhigh.blocked/
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Uri: Master | Next Rank: 500 Posts; Posts: 229; Joined: Tue Jan 13, 2009 6:56 am; Thanked: 8 times; GMAT Score:700

Re: Algebra question

by Uri » Thu Apr 30, 2009 10:10 pm

ornelaspedro wrote:For which of the following functions is f(a+b) = f(a) + f(b) for all positive numbers a and b?

The answer is -3x. Could anybody show me how to get to the answer.

are u sure that u have copied the entire problem?

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