1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Vector Functions

  1. Oct 3, 2013 #1
    1. The problem statement, all variables and given/known data
    Graph the curve with the parametric equations

    x=√(1-0.25cos^2(10t)) * cost
    y=√(1-0.25cos^2(10t)) * sint

    explain the appearance of the graph by showing that it lies on a sphere

    2. Relevant equations

    3. The attempt at a solution
    could anyone please just point me in the right direction on how to start this problem? any help would be greatly appreciated! thanks pf!
  2. jcsd
  3. Oct 3, 2013 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    'Graph the curve' seems pretty straightforward. Did you do that?

    Did you manipulate the parametric equations for x, y, and z to see if you can obtain the equation of a sphere?

    That would be pretty conclusive if you did.
  4. Oct 3, 2013 #3
    A sphere is the set of points equidistant from the same point. If a sphere has radius R, what equation in x,y,z describes it? Take the x, y, z you were given, with the assorted sines and cosines and see what happens when you plug those variables into the equation of a sphere.

    As far as graphing, I am a lousy artist, but if I had to graph it I'd sketch 3-d coordinates and graph some points based on cartesian x, y and z. This is maybe cheating, but I can't think too well in terms of cos 10t. The 10t will turn out to be irrelevant anyway-- try paragraph 1 and you'll see.
  5. Oct 3, 2013 #4
    thank you brmath and steamking! brmath...that's exactly what I am trying now. I am plugging in x, y, and z into the equation of a sphere and seeing if my t's cancel and the equation is satisfied.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted