Parametrization of a curve(the intersection of two surfaces)

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Homework Help Overview

The discussion revolves around finding the parametrization of a curve defined by the intersection of two surfaces given by the equations z=x^2-y^2 and z=x^2+xy-1. Participants are exploring how to express the variables in terms of a single parameter.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the difficulty in separating variables to find parametric equations. There are attempts to define one variable in terms of another, with some suggesting specific forms for x and y. Questions arise about the correctness of the parametrization and the relationship between curves and surfaces.

Discussion Status

Several participants have offered different parametrizations and expressed uncertainty about their validity. There is an ongoing exploration of the definitions and relationships involved in parametrizing curves versus surfaces, with some expressing a desire for clarification on their approaches.

Contextual Notes

Participants mention constraints such as the need for the parameter t to not equal zero and the potential for typographical errors in the expressions for z. There is a focus on understanding the concept of parametrization in the context of the given equations.

BennyT
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Homework Statement


I am looking to find the parametrization of the curve found by the intersection of two surfaces. The surfaces are defined by the following equations: z=x^2-y^2 and z=x^2+xy-1

Homework Equations

The Attempt at a Solution


I can't seem to separate the variables well enough to find parametric equations of this curve. I really don't like asking for answers on homework, but help defining one of the variables would be appreciated.
 
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Solve easily for x=f(y). Paremetrization will be y=t, x=f(t).
 
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Delta² said:
Solve easily for x=f(y). Paremetrization will be y=t, x=f(t).
So I already have x=(1/y)-y^2 and y=t and therefore x=(1-t^2)/t. Then z=(1-2t)/t^2. Is this the parametrization? If so, I have been sitting here for hours trying to find a trig relationship. It just looks too simple.
 
The parametrization of a curve is done with 1 variable t, but the parametrization of a surface needs 2 variables.
 
Delta² said:
The parametrization of a curve is done with 1 variable t, but the parametrization of a surface needs 2 variables.
Wait, so am I thinking about my parametrization wrong? Can I not define x, y, and z in terms of parameter t? In what ways is my answer wrong for my parametrization? I'm sorry if I'm asking so many quick questions but I really would like to understand this concept. So I had solved to x(t), y(t), and z(t) by manipulating the equations of two surfaces, z=x^2-y^2 and z=x^2+xy-1, and from this is gained a parametrization of x(t)=(1-t^2)/t, y(t)=t, and z(t)=(1-2t)/t^2 and I write this as r(t)=<x(t),y(t),z(t)> which is defined when t does not equal 0. Thank you for all your help so far.
 
Ok i just thought you were trying to parametrize the surface z=... but i see now what you were after.
 
Delta² said:
Ok i just thought you were trying to parametrize the surface z=... but i see now what you were after.
So this form I found is a good final form? I feel like I'm missing something? Thank you for everything! If this is true I can finally sleep before work!
 
slight mistake for z(t) it should be z(t)=(1-2t^2)/t^2. i guess probably a typo.
 

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