1. ## 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

2. Originally Posted by cuteisa89
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 $\displaystyle \theta$ = -pi/2?"

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

-Dan

3. Yeah.... t= θ.
Thanks I think I've got it now. I just wasn't sure how to do it properly.
Thanks Dan!

4. Originally Posted by cuteisa89
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: