Proving Inequality for Linear Functions: |h(h(x))+h(h(1/x))|>2

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Homework Help Overview

The discussion revolves around proving an inequality involving a function defined as the ratio of two distinct linear functions, specifically focusing on the behavior of the function h(x) = f(x)/g(x) where f and g map the interval [-1,1] onto [0,2]. The inequality to be proven is |h(h(x)) + h(h(1/x))| > 2.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the definitions of the linear functions f and g, considering their forms and the implications for the function h. There is discussion about the specific linear functions that satisfy the mapping condition, with suggestions that f(x) = 1+x and g(x) = 1-x could be valid choices. Questions arise regarding the simplification of h(1/x) and the algebra involved in proving the inequality.

Discussion Status

Participants have identified specific linear functions and are working through the implications of these choices on the function h. There is ongoing exploration of the algebraic manipulations required to approach the inequality, with some participants suggesting alternative methods such as calculus for further analysis. No consensus has been reached yet, and multiple interpretations of the problem are being considered.

Contextual Notes

There is an emphasis on the distinctness of the linear functions and their specific mapping properties. Participants note that there are only two distinct linear functions that meet the criteria, which may limit the scope of the discussion. The algebraic complexity of the problem is acknowledged, with participants questioning each other's calculations.

utkarshakash
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Homework Statement


If f and g are two distinct linear functions defined on R such that they map[-1,1] onto [0,2] and h:R-{-1,0,1}→R defined by h(x)=f(x)/g(x) then show that |h(h(x))+h(h(1/x))|>2

Homework Equations



The Attempt at a Solution


I assume f(x) to be ax+b and g(x) to be lx+m so that h(x) is (ax+b)/(lx+m). From here I can write h(h(x)) and h(h(1/x)) but there is nothing I can see that will help me to prove this inequality. Any ideas?
 
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utkarshakash said:

Homework Statement


If f and g are two distinct linear functions defined on R such that they map[-1,1] onto [0,2] and h:R-{-1,0,1}→R defined by h(x)=f(x)/g(x) then show that |h(h(x))+h(h(1/x))|>2

Homework Equations



The Attempt at a Solution


I assume f(x) to be ax+b and g(x) to be lx+m so that h(x) is (ax+b)/(lx+m). From here I can write h(h(x)) and h(h(1/x)) but there is nothing I can see that will help me to prove this inequality. Any ideas?
You can be more specific regarding the functions, f & g .

There are only two distinct linear functions which map [-1,1] onto [0,2] .

What are they?
 
SammyS said:
You can be more specific regarding the functions, f & g .

There are only two distinct linear functions which map [-1,1] onto [0,2] .

What are they?

y=x+1 and y=-x+1. Are these correct?
 
utkarshakash said:
y=x+1 and y=-x+1. Are these correct?
Yes. Equivalently, y=1+x and y=1-x .

So, there are only two cases to consider.

Choosing f(x) = 1+x and g(x) = 1-x, for now, what is h(1/x) ?
 
SammyS said:
Yes. Equivalently, y=1+x and y=1-x .

So, there are only two cases to consider.

Choosing f(x) = 1+x and g(x) = 1-x, for now, what is h(1/x) ?

x+1/x-1 which can be reduced to -f(x)/g(x)

And after simplifying further I am left with proving this inequality

|x-(1/x)|>2
 
Last edited:
utkarshakash said:
x+1/x-1 which can be reduced to -f(x)/g(x)
It looks like you get h(1/x) = -f(x)/g(x), for either way of assigning 1-x and 1+x to f(x) and g(x).
And after simplifying further I am left with proving this inequality

|x-(1/x)|>2

I got something similar to x-(1/x), but it is different.

Check your algebra.

It seems to me that one could do this more abstractly using some calculus, etc. (Maybe the Calculus part comes in the next step)
 

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