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# C4 parametric question watch

1. There are two questions I just can't do! The questions are : obtain a single Cartesian equation for each pair of parametric equations.. (1) X= t/t-1 and y = t/t+1. The second one is x= 2t/2t-3 and y = t/t+1
2. (Original post by Remainresilient_)
There are two questions I just can't do! The questions are : obtain a single Cartesian equation for each pair of parametric equations.. (1) X= t/t-1 and y = t/t+1. The second one is x= 2t/2t-3 and y = t/t+1
for 1) consider

(and for 2, in fact)
3. You always want the same denominators on the fractions so that you add or substract them easily and hence find the Cartesian equation.
4. Or it is just possible to solve for t directly from the x-equation, then put it into the y-equation.
e.g. (1) x=t/(t-1) -> xt-x=t -> t(x-1)=x -> t=x/x-1. Thus y=(x/x-1)/((x/x-1)+1), then simplify.
5. (Original post by constellarknight)
Or it is just possible to solve for t directly from the x-equation, then put it into the y-equation.
e.g. (1) x=t/(t-1) -> xt-x=t -> t(x-1)=x -> t=x/x-1. Thus y=(x/x-1)/((x/x-1)+1), then simplify.
If you can find t in terms of x or y, then yes you can just substitute it into the other equation. Sometimes it may make the simplification a lot more difficult.
6. (Original post by constellarknight)
Or it is just possible to solve for t directly from the x-equation, then put it into the y-equation.
e.g. (1) x=t/(t-1) -> xt-x=t -> t(x-1)=x -> t=x/x-1. Thus y=(x/x-1)/((x/x-1)+1), then simplify.
(Original post by B_9710)
If you can find t in terms of x or y, then yes you can just substitute it into the other equation. Sometimes it may make the simplification a lot more difficult.
I want to see a fight to the bitter end ....
7. (Original post by TeeEm)
I want to see a fight to the bitter end ....
In this case directly finding t is quite straightforward though.
8. (Original post by constellarknight)
In this case directly finding t is quite straightforward though.
if he does not reply you won ....
9. Also see my reply to the other thread on graph transformations: an OCR MEI examiner's report says candidates must say "one-way stretch", not "squash" or "squeeze".

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