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pleas help....function question

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Newbie | Next Rank: 10 Posts
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pleas help....function question

by bushra » Thu Dec 06, 2007 4:00 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 (x square)
b) f(x) =x+1
c) f(x) = root x
d) f(x) = 2/x
e) f(x) = -3x

i really dont have any idea how to solve this...please help...
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by Suyog » Thu Dec 06, 2007 4:11 pm
Let a = 2, b = 5, a+b = 7

1. f(x) = x^2 so f(a) = 4, f(b) = 25 and a + b = 29
but, f(a+b) = 49, No

2. f(x) = x + 1 so f(a) = 3, f(b) = 7 and a + b = 10
but, f(a+b) = 9, No

3. N0

4. N0

5. f(x) = -3x so f(a) = -6, f(b) = -15 and a + b = -21
Similarly f(a+b) = f(7) = -21

ans E.
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thanks suyog

by bushra » Thu Dec 06, 2007 5:14 pm
thanks a bundle suyog...i aways have problem with these types of questions...have taken GMAT 2 weeks back...got 570...so am retaking again on jan 18....thanks again...
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by moreonalps » Tue Dec 18, 2007 7:48 pm
Is E the right answer..question is asking f(a+b)=f(a)=(b)

evaluating for E as per Suyog, f(a+b)=-21;f(a)=-6;f(b)=-15..so, how does f(a+b)=f(a)=f(b)..

Please explain..
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by camitava » Wed Dec 19, 2007 1:25 am
moreonalps, u r correct but in the Qs itself it is saying that f(a + b) = f(a) = f(b). It should be f(a + b) = f(a) + f(b). Oooppppppsssss! Ok! This is solely my understanding and I personally assume this from the solution offered by Suyog. Suyog, am I wrong?
Correct me If I am wrong


Regards,

Amitava
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by Suyog » Wed Dec 19, 2007 4:42 am
you are right Camitava..

I had solved something like this earlier while practicing....
and it was f(a+b) = f(a) + f(b)
So i solved considering that.. LOL :)

bushra, can u pls confirm the question...
Thanks guys!
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by svijay800 » Thu Dec 20, 2007 3:31 am
Should have been f(a+b) = f(a)+f(b) for sure, otherwise none of the choices will hold true
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by Bschool08 » Sun Dec 23, 2007 9:26 pm
Just as an FYI

https://www.beatthegmat.com/08app-t7424.html
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