Find and verify parametric equations for an ellipse

In summary: If the problem is just asking for verification of the parametrization, you can just substitute the expressions for x and y into the equation for the ellipse. What do you get? If the statement you arrive at is always true, you have verified the parametrization you were given.
  • #1
the.flea
23
0

Homework Statement


Find and verify parametric equations for an ellipse.


Homework Equations


x=acost
y=bsint

The Attempt at a Solution



lets say the equation is x=3cost, y=3sint, domain: 0 to 2pi

x2 y2
-- + -- = 1
a2 b2

point does verify when t=0 x=3, y=0 which =1
any help?
 
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  • #2
Are you asking about the conversion of the equation for the ellipse from rectangular (Cartesian) to polar coordinates? You already have the first step: your parameterization is actually using polar coordinates, where the angle [tex]\theta[/tex] is expressed as a function of time t (in the simplest possible way, [tex]\theta = t[/tex] ).

If you substitute your expressions for x and y into the rectangular form of the equation, some work with trig identities will get you to a polar form.
 
  • #3
I'm sorry I do not understand. Please simplify the sentence.
There is a question asking to find and verify parametric equations for an ellipse. How would we start and finish such a complex question? Thank you in advance.
 
  • #4
I think I understand most of what you are saying, however I am not trying to go from rectangular to polar, I just want to verify this in rectangular form.
 
  • #5
the.flea said:
I think I understand most of what you are saying, however I am not trying to go from rectangular to polar, I just want to verify this in rectangular form.

I took back my last posting because I wasn't sure what you were asking for. If the problem is just asking for verification of the parametrization, you can just substitute the expressions for x and y into the equation for the ellipse. What do you get? If the statement you arrive at is always true, you have verified the parametrization you were given.

What I was wondering is whether they wanted you to use the polar equation

r^2 = x^2 + y^2

and simplify the result into a function r = r(t). But maybe that's more than they're looking for.
 
  • #6
… just plug'n'play …

the.flea said:
x=acost
y=bsint

x2 y2
-- + -- = 1
a2 b2

Hi, tiny flea! :smile:

If you're supposed to prove that x=acost, y=bsint satisfies x2/a2 + y2/b2 = 1, why don't you just plug those parametric values for x and y into the equation, and confirm that it is correct?

What is worrying you about that? :smile:
 

Related to Find and verify parametric equations for an ellipse

1. What is an ellipse?

An ellipse is a type of closed curve shape, similar to a circle, that is formed by the intersection of a cone and a plane. It has two foci and its shape can be described using two parameters - the major axis and the minor axis.

2. How do you find the parametric equations for an ellipse?

The parametric equations for an ellipse can be found by using the cosine and sine functions to represent the x and y coordinates of points on the ellipse. The equations can be written as x = a*cos(t) and y = b*sin(t), where a and b are the lengths of the semi-major and semi-minor axes, and t is the parameter that varies between 0 and 2π.

3. What is the role of the parameter t in the parametric equations for an ellipse?

The parameter t in the parametric equations for an ellipse represents the angle of rotation around the center of the ellipse. As t increases from 0 to 2π, the point (x, y) moves along the ellipse in a counterclockwise direction.

4. How do you verify that the parametric equations represent an ellipse?

To verify that the parametric equations represent an ellipse, you can use the distance formula to find the distance between any point (x, y) on the ellipse and the foci. If the distance is constant, then the point lies on the ellipse. You can also graph the parametric equations and see that they form a closed curve with two foci.

5. Can parametric equations be used to find the area of an ellipse?

Yes, parametric equations can be used to find the area of an ellipse. The formula for the area of an ellipse is A = π*a*b, where a and b are the lengths of the semi-major and semi-minor axes. By finding the integral of the parametric equations x = a*cos(t) and y = b*sin(t), the area of the ellipse can be calculated as the definite integral from 0 to 2π of the equation π*a*b*sin(t)*cos(t) dt.

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