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Math Help - Parametric equations

  1. #1
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    Post Parametric equations

    Hi,
    I'm completely lost in this problem .... can someone help me pls?

    Consider the parametric equations x= 4*cos^2(θ) and y = 2*sin(θ)

    and fill this chart.

    When t = -pi/2, x = ? and y = ?
    When t = -pi/4, x = ? and y = ?
    When t = pi/4, x = ? and y = ?
    When t = pi/2, x = ? and y = ?

    I also have to graph the equation in my pgrahing calculator. I tried to do it but I don't know if I did it right.


    - Isabel
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  2. #2
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by cuteisa89 View Post
    Hi,
    I'm completely lost in this problem .... can someone help me pls?

    Consider the parametric equations x= 4*cos^2(θ) and y = 2*sin(θ)

    and fill this chart.

    When t = -pi/2, x = ? and y = ?
    When t = -pi/4, x = ? and y = ?
    When t = pi/4, x = ? and y = ?
    When t = pi/2, x = ? and y = ?

    I also have to graph the equation in my pgrahing calculator. I tried to do it but I don't know if I did it right.


    - Isabel
    When you say "When t = -pi/2" do you mean "When \theta = -pi/2?"

    Just plug the angle into the given formulas for x and y.
    For example:
    \theta = \pi/2 \implies x = 4cos^2(\pi/2) = 0 \text{ and }y = 2sin(\pi/2) = 2

    -Dan
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  3. #3
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    Post

    Yeah.... t= θ.
    Thanks I think I've got it now. I just wasn't sure how to do it properly.
    Thanks Dan!
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  4. #4
    Member
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    Quote Originally Posted by cuteisa89 View Post
    Hi,
    I'm completely lost in this problem .... can someone help me pls?

    Consider the parametric equations x= 4*cos^2(θ) and y = 2*sin(θ)

    and fill this chart.

    When t = -pi/2, x = ? and y = ?
    When t = -pi/4, x = ? and y = ?
    When t = pi/4, x = ? and y = ?
    When t = pi/2, x = ? and y = ?

    I also have to graph the equation in my pgrahing calculator. I tried to do it but I don't know if I did it right.


    - Isabel
    x=4(cost)^2=4(1-(sint)^2)=4-(2sint)^2=4-y^2
    So it is a parabola like this:
    Attached Thumbnails Attached Thumbnails Parametric equations-july56.gif  
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