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# PS- GMAT Prep

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Intern
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21 Jun 2006, 21:36
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22 Jun 2006, 03:06
We have f(x)=-3x
so f(a)+f(b)=-3a-3b=-3*(a+b)=f(a+b)
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22 Jun 2006, 03:13
f(a+b)=f(a)+f(b) is true only for multiplication
therefore only the last is true f(x)=-3x
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22 Jun 2006, 08:57
duh! Thank you folks!

-Tru
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22 Jun 2006, 09:03
Clearly E.

-3(a+b) = -3a + (-3b)
f(a+b) = f(a) + f(b)
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22 Jun 2006, 15:04
Yup. E.

Hey, if you don't mind my asking, how much did you score on that test? Just curious...
_________________

Uh uh. I know what you're thinking. "Is the answer A, B, C, D or E?" Well to tell you the truth in all this excitement I kinda lost track myself. But you've gotta ask yourself one question: "Do I feel lucky?" Well, do ya, punk?

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22 Jun 2006, 17:01
guys, i am dumb on this one. i like to know every step on this one.
thankx..
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22 Jun 2006, 17:32
For given functions A..E we need one which is such that
f(a+b) = f(a) + f(b)

A. f(x) = x^2 i.e. f(a+b) = (a+b)^2
This is not equal to a^2 + b^2 = f(a) + f(b)

B. f(x) = x+1
f(a+b) = a+b+1
f(a) + f(b) = a+1 + b+1 = a+b+2 which is not eq. f(a+b)

C. f(x) = sqrt(x)
f(a+b) = sqrt(a+b) which is not eq. sqrt(a) + sqrt(b)

D. f(x) = 2/x
f(a+b) = 2/(a+b) which is not eq to 2/a + 2/b

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

Therefore E.

MA wrote:
guys, i am dumb on this one. i like to know every step on this one.
thankx..
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22 Jun 2006, 18:18
great. you guys are ginious.

now its pretty clear. thanx a ton again.

haas_mba07 wrote:
For given functions A..E we need one which is such that
f(a+b) = f(a) + f(b)

A. f(x) = x^2 i.e. f(a+b) = (a+b)^2
This is not equal to a^2 + b^2 = f(a) + f(b)

B. f(x) = x+1
f(a+b) = a+b+1
f(a) + f(b) = a+1 + b+1 = a+b+2 which is not eq. f(a+b)

C. f(x) = sqrt(x)
f(a+b) = sqrt(a+b) which is not eq. sqrt(a) + sqrt(b)

D. f(x) = 2/x
f(a+b) = 2/(a+b) which is not eq to 2/a + 2/b

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

Therefore E.
Re: PS- GMAT Prep   [#permalink] 22 Jun 2006, 18:18
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