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Homework Help: Some review problems

  1. Jan 24, 2012 #1
    1. The problem statement, all variables and given/known data

    I'm having some trouble remembering how to do this in a refresher course...

    sketch the intersection of (x^2)+(y^2)+(z^2)=3 and z<0
    sketch the intersection of z=2(x^2)+2(y^2) and z=4-(x^2)-(y^2)

    2. Relevant equations

    3. The attempt at a solution

    I think the first one is a circle with points at 1 and -1 on each axis, not too sure if there's a certain method I'm supposed to use to figure this out with though.
  2. jcsd
  3. Jan 24, 2012 #2


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    Homework Helper

    note quite... the first is the half the surface of a sphere below zero

    one way that may help is too look at the intesection with a plane (x=0,y=0,z=0) are good

    then you either need to recognise the form or think about how one viarable relates toteh other the other

    eg. for 2)



    these are both idenitical parabolas


    cuts in the cy planes give circles, so this a circular paraboloid,

    you should try drawing each of the parbaolas and a circle in 3D perspective on paper
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