Setting up a path for a line integral

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Discussion Overview

The discussion revolves around finding a path for a line integral that connects two points in the plane, specifically from $${(x_i, y_i)}$$ to $${(x_f, y_f)}$$. Participants explore different representations of the path and clarify the requirements for it to be a straight line.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant proposes a path defined by $${\mathbf{r}(t) = (x_f - x_i) \cos(t) \mathbf{i} + (y_f - y_i) \sin(t) \mathbf{j}}$$ but questions its correctness.
  • Another participant points out that the proposed path does not represent a straight line and suggests simply connecting the two points directly.
  • A different participant suggests a vector representation $${\mathbf{r} = (x_f - x_i) \mathbf{i} + (y_f - y_i) \mathbf{j}}$$ but notes it lacks a variable $${t}$$.
  • One participant emphasizes the need to define how to move along the line described by the vector and references a lecture on parametric equations for further clarification.
  • A later reply proposes that the path can be expressed parametrically as $${x = (x_f - x_i)t + x_i}$$ and $${y = (y_f - y_i)t + y_i}$$, confirming it meets the conditions for $${t = 0}$$ and $${t = 1}$$.

Areas of Agreement / Disagreement

Participants express disagreement regarding the initial proposed path, with some advocating for a more straightforward representation of the straight line connecting the two points. The discussion remains unresolved as multiple approaches are presented without consensus on the best method.

Contextual Notes

There is ambiguity regarding the correct representation of the path, particularly in how to incorporate the parameter $${t}$$ effectively. Some participants highlight the need for clarity in defining the movement along the line.

hivesaeed4
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If $${C}$$ is the straight line that connects points in the plane $${(x_i, y_i)}$$ and $${(x_f, y_f)}$$, find a path $${\tmmathbf{r} (t)}$$ that traces out $${C}$$ starting at the initial point $${(x_i, y_i)}$$ and ending at $${(x_f, y_f)}$$ as $${t}$$ goes from zero to 1.

Now the path that I've been able to come up with is

r=(xf-xi)cos(t) i +(yf-yi)sin(t) j

Note r is a vector giving the path and i and j are the unit vectors.

Is my path correct or is their some error in it?
 
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hivesaeed4 said:
If $${C}$$ is the straight line that connects points in the plane $${(x_i, y_i)}$$ and $${(x_f, y_f)}$$, find a path $${\tmmathbf{r} (t)}$$ that traces out $${C}$$ starting at the initial point $${(x_i, y_i)}$$ and ending at $${(x_f, y_f)}$$ as $${t}$$ goes from zero to 1.

Now the path that I've been able to come up with is

r=(xf-xi)cos(t) i +(yf-yi)sin(t) j

Note r is a vector giving the path and i and j are the unit vectors.

Is my path correct or is their some error in it?


I must be misunderstanding something as the path you described above is NOT a straight one, as you required at the beginning...

Question: why not simply take the straight line connecting the two points??

DonAntonio
 
So the path should be something like:

r=(xf-xi)i + (yf-yi) j ?
 
The problem is you have simply defined a vector and not how one would move along the line the vector is describing (which is quite straight forward, how would you do this?). If you're having trouble i came across a lecture on parametric equations for lines by denis auroux at mit (in youtube lecture 5 mit course on multivariable calculus, the first 10 mins will do for you)

Hope this helps.
 
hivesaeed4 said:
So the path should be something like:

r=(xf-xi)i + (yf-yi) j ?
That is a vector from (xi, yi) to (xf, yf)- which doesn't have a variable "t". The path itself would be x= (xf- xi)t+ xi, y= (yf- yi)t+ yi. You can see that is right by taking t= 0 and t= 1.
 

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