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GMATPrep - Difficult Functions Question

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by tutonaranjo » Tue Aug 28, 2007 6:04 pm
Can someone explain this in detail? No idea how these function questions work.

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) = sqrt x
d) f(x) = 2/x
e) f(x) = -3x

Answer is E
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Source: — Problem Solving |

RE: GMATPrep - Difficult Functions Question

by speed » Tue Aug 28, 2007 11:15 pm
put a=1 , b=1

for choice a) f(x) = x^2 ; f(a) = 1. f(b) =1, f(a+b) = (1+1)^2=2^2 no match

similarly other choices too have LHS != RHS EXCEPT CHOICE E

ANSWER IS (E)
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by kajcha » Wed Aug 29, 2007 10:54 am
IMO, the best approach to solve such problems is to substitute numbers.
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