A function is on action.

Algebra Level 3

A continuous function f(x) on R R R\rightarrow R satisfies the relation f ( x ) + f ( 2 x + y ) + 5 x y = f ( 3 x y ) + 2 x 2 + 1 f(x)+f(2x+y)+5xy=f(3x-y)+2x^{2}+1 where x , y R x,y€R then which of the options are correct?

1. f(x) is an even function.

2. f(x) is an odd function.

3. f(x) is many-one .

4. f(x) is one-one.

5. f(x) is neither even nor odd.

1,3 3,5 2,4 2,3

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1 solution

Arghyanil Dey
May 19, 2014

The given condition is f ( x ) + f ( 2 x + y ) + 5 x y = f ( 3 x y ) + 2 x 2 + 1 f(x)+f(2x+y)+5xy=f(3x-y)+2x^{2}+1 At first put x=y=0 in the given equation, then we get f ( 0 ) = 1 f(0)=1 . If we put 2 x = y 2x=-y we get f ( x ) + f ( 0 ) + 5 x × ( 2 x ) = f ( 5 x ) + 2 x 2 + 1 f(x)+f(0)+5x×(-2x)=f(5x)+2x^{2}+1 f ( x ) f ( 5 x ) = 12 x 2 f(x)-f(5x)=12x^{2} ......... 1

If we put 3 x = y 3x=y we get f ( x ) + f ( 5 x ) + 15 x 2 = f ( 0 ) + 2 x 2 + 1 f(x)+f(5x)+15x^{2}=f(0)+2x^{2}+1 f ( x ) + f ( 5 x ) = 2 13 x 2 f(x)+f(5x)=2-13x^{2} .............. 2

If we add 1 & 2 we get f ( x ) = 1 x 2 2 f(x)=1-\frac{x^{2}}{2} The result suggests that the function is even as well as many-one.

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