Intersection of Surfaces

  • Thread starter cp255
  • Start date
  • #1
54
0
I need to find a parametric equation of the vector function which is the intersection of y = x2 and x2 + 4y2 + 4z2=16. I know the graph of the first equation is a parabola which stretches from negative infinity to infinity in the z direction. I also know that the second equation is that of an ellipsoid.

I have attempted to solve this by substituting x2 for y in the second equation which I think produces an ellipse. After this I am stuck.
 

Answers and Replies

  • #2
Dick
Science Advisor
Homework Helper
26,260
619
I need to find a parametric equation of the vector function which is the intersection of y = x2 and x2 + 4y2 + 4z2=16. I know the graph of the first equation is a parabola which stretches from negative infinity to infinity in the z direction. I also know that the second equation is that of an ellipsoid.

I have attempted to solve this by substituting x2 for y in the second equation which I think produces an ellipse. After this I am stuck.
You want a PARAMETRIC form. You want to express x, y and z in terms of some parameter t. I would pick x=t to start. Now can you express the other variables in terms of t?
 
  • #3
418
28
edit: why can't I delete my post? No replies yet. But yeah, take Dick's suggestion for a straightforward way to think about this problem.
 
  • #4
54
0
So I took Dick's approach and I got <t, t2, (1/2)(16 - t2 - 4t4)1/2>. The only problem is that this is half the solution. I know I could get the other half if I took the negative sqrt but for my class I need one equation. It's kind of like when you convert the circle x2 + y2 = 1 to a parametric form; you could get <t, (1-t2)1/2> which just gives you half the circle, or you can do it the better way and get <sin(t), cos(t)> which gives an entire circle.
 
  • #5
115
2
cp255, by substitution ##y=x^2## you got the ellipse equation. Complete the square and it will be easy to parametrize with ##\cos t,\,\sin t##
 
  • #6
54
0
I know but then still I would have to define x as the square root of what y which only gives half the curve.
 

Related Threads on Intersection of Surfaces

  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
2
Views
2K
Replies
10
Views
6K
  • Last Post
Replies
1
Views
2K
Replies
1
Views
10K
  • Last Post
Replies
2
Views
7K
Replies
8
Views
2K
  • Last Post
Replies
0
Views
1K
Replies
3
Views
672
Replies
4
Views
6K
Top