You have to look for f(x+y)=f(x)+f(y)
Solution has to be simple i.e. no squares, divisions, additions
If you don't immediatly see that E is the solution, plug in numbers
x=3, y=2
You will find that E is the right answer
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f(x) problem
Source: Beat The GMAT — Problem Solving |
Well, where is y? Are you saying to apply x for a, y for b? still I do not see how -3x applies to the given f(a+b)=f(a)+f(b)....help me there!
THANKS! :roll:
THANKS! :roll:
Sorry for using x, y .. was a,b
For f(x)=-3x
a=2
b=3
f(a+b)=f(5)=-3*5
f(a)+f(b)=-3*2+-3*3=-15
Therefore E is the right answer
Does not work for any function were x is x^2, 1/x as not linear
Try
For f(x)=x^2
a=2
b=3
f(a+b)=f(5)=5^2=25
f(a)+f(b)=2^2+3^2=13
or
For f(x)=2/x
a=2
b=3
f(a+b)=f(5)=2/5
f(a)+f(b)=2/2+2/3
For f(x)=-3x
a=2
b=3
f(a+b)=f(5)=-3*5
f(a)+f(b)=-3*2+-3*3=-15
Therefore E is the right answer
Does not work for any function were x is x^2, 1/x as not linear
Try
For f(x)=x^2
a=2
b=3
f(a+b)=f(5)=5^2=25
f(a)+f(b)=2^2+3^2=13
or
For f(x)=2/x
a=2
b=3
f(a+b)=f(5)=2/5
f(a)+f(b)=2/2+2/3
