Parametric Equations Homework - Find Curve & Position Vector

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Homework Help Overview

The discussion revolves around finding parametric equations for the curve of intersection of two cylinders defined by the equations \(x^2+y^2=4\) and \(z+x^2=4\). Participants are exploring how to express the curve parametrically and derive a position vector from these equations.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss various choices for the parameter \(t\), including using \(t=x\) and \(t\) as the angular coordinate in the \(x,y\) plane. There are questions about the appropriateness of these choices and the implications for the resulting equations.

Discussion Status

There is an ongoing exploration of different parametrizations, with some participants suggesting polar coordinates as a viable approach. While attempts have been made to derive the position vector, there is no consensus on the correctness of the expressions being proposed.

Contextual Notes

Participants note the challenge of defining the curve due to the presence of square roots when using certain parameterizations. There is also mention of the need to visualize the curve to aid in selecting an appropriate parameter.

chrsr34
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Homework Statement


Consider the curve of intersection of the cylinders [x^2+y^2=4] and [z+x^2=4]. Find parametric equations for this curve and use them to write a position vector.

Homework Equations


Thats what I am looking for. What to set t equal to.


The Attempt at a Solution


I set t=x and got a square root for y. So if i set t=x^2, i get rid of the square root for y, but I am not sure if this is correct. i really don't know the rules for parametric equations. Any input is appreciated.

Chris
 
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An easy choice for t is the angular coordinate in the x,y plane. So x=2*cos(t), y=2*sin(t). Given this, can you figure out what z is in terms of t? Unfortunately, I don't think there are any general rules for doing this. You just have to make a picture in your mind of what the curve looks like and then look for a choice for t.
 
I see. Yes i could find z with those coordinates. But is there a reason you chose those? Are those cylindrical coordinates? (im a little rusty).
Is there anything wrong with setting t=x^2?
 
The x^2+y^2=4 cylinder intersects the x,y plane in a circle. It's easy to parametrize that in polar coordinates. If you take t=x^2 then you still have a square root for y (contrary to what you said), so you'd have to define the curve as a union of pieces.
 
All yes your right.
So my position vector should be: r = < 4cos^2(t), 4sin^2(t), 4-4cos^2(t) >
Is this correct?
 
Noooo. x=2*cos(t), not 4cos^2(t)!
 
yea i just realized i did that.
So, r = < 2cos(t), 2sin(t), 4-4cos^2(t) >

This look good?
 

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