easy one:)
f(a+b) should be equal to f(a) + f(b)
now, its only possible when f(x)=-3x
f(a)=-3(a)
f(b)=-3(b)
add the two
f(a)+f(b)=-3(a+b)=f(a+b)
is it clear now?
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f(a+b)
Source: Beat The GMAT — Problem Solving |
Many of the great achievements of the world were accomplished by tired and discouraged men who kept on working.
Pls let me know How you arrived at A?
shibal wrote:not really... could u pls give more details?
Many of the great achievements of the world were accomplished by tired and discouraged men who kept on working.
Substitute #'s, say a=2 and b=4.
For example for the first one:
(2+4)^2 and 2^2 +4^2.
The two equations are not equal.
Only E satisfies the requirement.
For example for the first one:
(2+4)^2 and 2^2 +4^2.
The two equations are not equal.
Only E satisfies the requirement.
You have to plug in (a + b) in place of x and see if both the sides match.
Lets take A - f(x) = x^2
x = (a + b), x = a, x = b
L.H.S - f(a + b) = (a + b)^2
R.H.S - f(a) + f(b) = a^2 + b^2
therefore L.H.S is not equal to R.H.S
follow the same thing for rest of the answer choices and you'll get the right answer.
Lets take A - f(x) = x^2
x = (a + b), x = a, x = b
L.H.S - f(a + b) = (a + b)^2
R.H.S - f(a) + f(b) = a^2 + b^2
therefore L.H.S is not equal to R.H.S
follow the same thing for rest of the answer choices and you'll get the right answer.
shibal wrote:i'm sorry, but i can't see how to do this one....
I think, we can go to correct option by doing trail and error by substituting some values and check it..
E option will be the only correct option if one goes by that way.
E option will be the only correct option if one goes by that way.
