Quick Parametric Question (Basic) (1 Viewer)

[StudyOnly]

So I have this question, from basic parametrics ... Only need help in part b

1) Write the coordinates of the focus and equation of the directrix of:
a) x = -12t and y = -6t²
then,
b) Find the points on the parabola when t = +2, -2

Now the question is regarding b)

If I sub t = +2, -2 into x =-12t and y = -6t²
I get -24, -24 when t = 2
and 24, - 24 when t = -2

However, When I sub t = +2, -2 into x = 2at and y = at²
I get 24, 24 when t = 2
and -24, 24 when t = -2

Shouldn't they both give the same answer?

The second bit of working was done by a tutor, and I simplly copied it down from the board ... I think they should have used x = -2at and y = -at² not the positive versions. I might be wrong so thats why I'm asking for help. Thanks

 

[fan96]

Shouldn't they both give the same answer?

No - your two equations are





(given )

These are two different parabolas.

If you wanted the same answer, then yes, you would have to use .

 

[StudyOnly]

Thanks,

So the correct answer would be

-24, -24 when t = 2
and 24, - 24 when t = -2

Right?

 

[fan96]

Thanks,

So the correct answer would be

-24, -24 when t = 2
and 24, - 24 when t = -2

Right?

Yes.

 

[StudyOnly]

Thanks Again