Conics (2 Viewers)

[Lukybear]

If they ask for the cartesian equn of an elipps, with x=3cost, y=2cost

Would it be sufficent to say
a=3, b=2
thus
x^2/9 + y^2/4 = 1

 

[bleaver]

Yes that would be fine.
In that kind of question, they're just looking to see that you recognise the structure of the parametrics.
You could state that the parametrics are x=acost, y=bsint. And therefore a=...etc
But it would make no difference in terms of marks.

 

[Lukybear]

Also... can some1 explain to me why the parametric equn of hyperbola has limited range:

ie. -pi < theta < pi, and if P is on the left branch, -pi < theta < -pi/2, pi / 2< theta < pi