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Homework Help: Parametric equation true/false

  1. Mar 25, 2009 #1
    1. The problem statement, all variables and given/known data

    (a) The parametric curve x = (3t + 4)2, y = (3t + 4)2 - 9 for 0 t 3 is a line segment.
    (b) A parameterization of the graph of y = lnx for x > 0 is given by x = et, y = t for - < t < .
    (c) The line parameterized by x = 8, y = 5t, z = 6 + t is parallel to the x-axis.

    2. Relevant equations

    3. The attempt at a solution

    a. false
    b. true
    c. true

    Is my answer correct? If its false can someone help me to explain why
  2. jcsd
  3. Mar 26, 2009 #2
    You should provide the reasoning behind your answers.
  4. Mar 26, 2009 #3
    for part a, it's just a mere guess as I see a ^2 there, so I thought it wouldn't be a line
    for part b I think because when you plugged in the graph you get the same
    for part c, the two lines aren't multiples of each other... 5j + k and 1i
  5. Jun 9, 2011 #4
    was your answer correct?
  6. Jun 9, 2011 #5

    Char. Limit

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    Gold Member

    For equation 1, try finding an equation for y in terms of x. It should be pretty easy. Then you'll easily see whether it's a line or not.
  7. Jun 10, 2011 #6


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    Science Advisor

    Actually, the way you wrote it, there is NO "^2".
    A way of seeing that it is not a line is to choose three values of t giving three points on the graph. Find the slopes between two pairs of points. If they are not the same, it is not a line.

    That sentence doesn't make sense to me. How do "plug in" a graph? And what does "the same" refer to?

    Because the "two lines aren't multiples of each other", you say the line is parallel to the x-axis?
    Last edited by a moderator: Jun 10, 2011
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