Domains Were Never This Tough!!!

Algebra Level 5

A function f is non-negative and defined on an appropriate subset of Real Numbers . If

x 2 f ( x ) + f ( 1 x ) = 2 x x 4 { x }^{ 2 }f\left( x \right) \quad +\quad f(1-x)\quad =\quad 2x-{ x }^{ 4 }

is true for all x on the domain , then find largest interval of values of x as [a,b]

What is The Value of [100(a+b)]

[x] represents the greatest integer function


The answer is 100.

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1 solution

Harsh Depal
Mar 13, 2014

f ( x ) 0 , ( F o r A l l V a l u e s O f x ) x 2 f ( x ) + f ( 1 x ) 0 , ( F o r A l l V a l u e s O f x ) 2 x x 4 0 S o l v i n g T h e I n e q u a l i t y W e G e t , x [ 0 , 2 1 / 3 ] S o , x m u s t b e i n t h e a b o v e r a n g e a n d 1 x m u s t a l s o b e i n t h e a b o v e r a n g e o n s o l v i n g t h a t w e g e t x [ 0 , 1 ] S o T h e A n s w e r I s 100 f\left( x \right) \quad \ge \quad 0\quad ,\quad (For\quad All\quad Values\quad Of\quad x)\\ { x }^{ 2 }f(x)\quad +\quad f(1-x)\quad \ge \quad 0\quad ,\quad (For\quad All\quad Values\quad Of\quad x)\\ \therefore \quad 2x-{ x }^{ 4 }\quad \ge \quad 0\\ \quad Solving\quad The\quad Inequality\quad We\quad Get,\\ \quad \quad x\quad \in \quad [\quad 0\quad ,\quad { 2 }^{ 1/3 }]\\ So,\quad x\quad must\quad be\quad in\quad the\quad above\quad range\quad \\ and\quad 1-x\quad must\quad also\quad be\quad in\quad the\quad above\quad range\\ on\quad solving\quad that\quad we\quad get\\ x\quad \in \quad [0,1]\\ So\quad The\quad Answer\quad Is\quad \boxed { 100 }

why must 1- x be in that range too?

space sizzlers - 4 years, 3 months ago

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