How would I find a vector parametric equation through these points?

In summary: That would give you the equation for r(3) and r(8).@HallsofIvy and LCKurtz: Thanks, so basically I'm re-scaling the original linear equations to fit into the new parameters? Sorry, I'm just trying to understand the geometrical aspect.In summary, the problem is to rescale the original linear equations so that they fit into the new parameters t=3 and Q=8.
  • #1
SMA_01
218
0

Homework Statement



Find a vector parametric equation r(t) for the line through the points P=(3,0,4) and Q=(1,−3,9) for each of the given conditions on the parameter t.

I'm stuck on this one:

r(5)=P and r(8)=Q

Homework Equations





The Attempt at a Solution



I tried finding the parametric equations but it didn't work.

I don't really understand how to go about solving this. What is it asking exactly and how would I start?

Any help is appreciated.
 
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  • #2
Can you find any parametric equation of the line through those two points? Let's start there; then we can talk.
 
  • #3
@LCKurtz: Yeah I used the old method of finding the parametric equations, taking PQ as the vector, and using either P or Q as points. That didn't work out. I actually figured out how to do it, I just want to understand it. Like geometrically, what is the question saying?
 
  • #4
SMA_01 said:
@LCKurtz: Yeah I used the old method of finding the parametric equations, taking PQ as the vector, and using either P or Q as points. That didn't work out. I actually figured out how to do it, I just want to understand it. Like geometrically, what is the question saying?

The "standard" parametric equation with that direction vector and starting at P is at the point P when t = 0 and Q when t = 1. The point of the problem is to rescale the parameter t so that it is at point P when t = 3 and Q when t = 8.
 
  • #5
Suppose you just start with the general linear formulas x= at+ b, y= ct+ d, z= et+ f and use the facts that
x(5)= 3, y(5)= 0, z(5)= 4 and x(8)= 1, y(8)= −3, z(8)= 9.

You have three sets of two equations in two unknowns.
 
  • #6
@HallsofIvy and LCKurtz: Thanks, so basically I'm re-scaling the original linear equations to fit into the new parameters? Sorry, I'm just trying to understand the geometrical aspect.
 
  • #7
Well, a translation, to put "0" at "5", and then a scaling, to stretch "0 to 1" to "5 to 8".
 
  • #8
SMA_01 said:
@HallsofIvy and LCKurtz: Thanks, so basically I'm re-scaling the original linear equations to fit into the new parameters? Sorry, I'm just trying to understand the geometrical aspect.

Think about what happens if you take the "standard" equation starting at P and use PQ as the direction vector, but then replace t by (t-5)/3.
 

What is a vector parametric equation?

A vector parametric equation is a way to represent a line or curve in three-dimensional space using parameters. It is typically written in the form of r(t) = ai + bj + ck, where i, j, and k are unit vectors and a, b, and c are constants that determine the direction and position of the line or curve.

Why would I need to find a vector parametric equation?

A vector parametric equation is useful for representing and visualizing complex curves and surfaces, as well as for solving problems in physics, engineering, and other fields that involve motion or direction in three-dimensional space.

How do I find a vector parametric equation through a set of given points?

To find a vector parametric equation through a set of given points, you first need to determine the direction vector by subtracting the coordinates of one point from the coordinates of another point. Then, you can use the direction vector and one of the given points to create the parametric equation by plugging in the values for a, b, and c.

Can I use any two points to find a vector parametric equation?

No, you cannot use any two points to find a vector parametric equation. The points must be distinct and not lie on the same line or curve. Otherwise, the direction vector would be zero and the equation would not accurately represent the desired line or curve.

Are there alternative ways to represent a line or curve in three-dimensional space?

Yes, there are alternative ways to represent a line or curve in three-dimensional space, such as using a scalar parametric equation, a symmetric parametric equation, or a Cartesian equation. Each of these methods has its own advantages and may be more suitable for certain applications.

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