A simple functional equation

Algebra Level 4

Let f ( x ) f(x) be a function that satisfies

f ( 2014 + x ) = f ( 2014 x ) . f(2014 + x) = f(2014 - x) .

If f f has exactly 3 3 roots being α , β , γ \alpha, \beta, \gamma , what is the value of α + β + γ ? \alpha + \beta + \gamma ?


The answer is 6042.

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4 solutions

Joel Tan
Feb 19, 2014

The equation implies that if ( 2014 a ) (2014-a) is a root, ( 2014 + a ) (2014+a) must also be a root. However, the only way for there to be an odd number of roots is when a = 0 a=0 , otherwise there will be another distinct root. Thus one of the roots is 2014 and the rest are ( 2014 x ) (2014-x) , and ( 2014 + x ) (2014+x) for some real x x . Those two roots add up to 4028. Thus the answer is 6042.

You may state the main theme:

The equation is symmetric about x = 2014 \text{The equation is symmetric about } x=2014 .

A Brilliant Member - 7 years, 3 months ago

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When is an equation symmetric??

Satvik Golechha - 7 years, 3 months ago

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When it's behaviour is symmetric about a line or a point.

Rishik Jain - 3 years, 3 months ago
Aditya Raj
Mar 3, 2014

The equation implies that if (2014-a) is a root,(2014+a) must also be a root. However, the only way for there to be an odd number of roots is when a=0 , otherwise there will be another distinct root. Thus one of the roots is 2014 and the rest are (2014-x) , and (2014-x) for some real x. Those two roots add up to 4028. Thus the answer is 6042.

Plagiarism

Joel Tan - 6 years, 9 months ago
Musham Ranadheer
Feb 22, 2014

the function is symmetric about 2014 and 1 root is 2014

Eddie The Head
Feb 19, 2014

We have f ( x + 2014 ) = f ( 2014 x ) f(x+2014)=f(2014-x) f ( x ) = f ( 4028 x ) f(x)=f(4028-x) So whenever a a is a root of f ( x ) f(x) 4028 a 4028-a is also a root of f ( x ) f(x) let b be another root of the function which is not equal to a.This implies (4028-b) is also another distinct root...So the equation will have 4 roots instead of 3 which is a contradiction... So the only possibility is that all the roots must be equal so a = 4028 a a =4028-a ...and a = 2014 a = 2014

So the sum of all the roots is 2014 3 = 6042 2014*3 = 6042

OOPs...Abandon this solution I made an exaggerated assumption that all the roots must be equal but it is not so...It should have been actually b = 4028 b b = 4028 - b and the other two roots would have been a,2014-a....This condition would equally suffice....and of course it's a more generalized one....

Eddie The Head - 7 years, 3 months ago

YEAH- THE SOLUTION IS BIT TRICKY.NEVERTHELESS GOOD LOGIC.

Prabir Chaudhuri - 6 years, 7 months ago

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