Mapping D* onto a Triangle: Investigating One-to-One Functions

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Homework Help Overview

The problem involves determining the image set of a function T defined on the unit square D* = [0,1] x [0,1] and assessing whether T is a one-to-one function. The function is given by T(x*,y*) = (x*y*, x*).

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the nature of the function T and its one-to-one property, with some suggesting breaking D* into two functions to simplify the analysis. Questions arise regarding how to find the image set D and the implications of including the origin in the analysis.

Discussion Status

Some participants have proposed using parametric equations to explore the image set and have shared their findings regarding the vertices of the resulting shape. There is an acknowledgment of the challenges in determining the one-to-one nature of the function, particularly concerning specific points.

Contextual Notes

Participants are considering the implications of the function's behavior at the origin and how it affects the overall mapping. There is a focus on understanding the image set in relation to the defined function and the constraints of the problem.

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Homework Statement



Let D* = [0,1] x [0,1] and define T on D* by T(x*,y*) = (x*y*, x*). Determine the image set D. Is T one-to-one?

Homework Equations





The Attempt at a Solution



Okay... So I know it is not one to one, if you take out the point (x=0) then it is one-to-one, so you must be careful with the origin.
But I don't know how to find the image set D. Because there are two variables in the first component in T x and y*. How do I find D?
 
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hi der.physika! :smile:

it's easier if you break D* into two functions

what is the image of the function that sends (x, y) to (x, xy)?

(it may help to consider all the (x, 1)s)
 
tiny-tim said:
hi der.physika! :smile:

it's easier if you break D* into two functions

what is the image of the function that sends (x, y) to (x, xy)?

(it may help to consider all the (x, 1)s)


Okay... I think I found the solution

by using parametric equations

(t,0); (1,t); (t,1), (0,t) and plugging them in yields (0,0), (0,0), (t,t), (0,t) which makes it not 1 to 1. So... it gives me the triangle with those vertices. is this correct?
 
(just got up :zzz: …)
der.physika said:
… (t,0); (1,t); (t,1), (0,t) and plugging them in yields (0,0), (0,0), (t,t), (0,t) which makes it not 1 to 1. So... it gives me the triangle with those vertices. is this correct?

That's right! :smile:

(as you've seen, a short-cut that will work in any "non-folding" case is to simply find where all the corners go to :wink:)
 

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