Hey! Sign in to get help with your study questionsNew here? Join for free to post


Announcements Posted on
Why bother with a post grad? Are they even worth it? Have your say! 26-10-2016
    • Thread Starter

    why do we substitute t values back into P(at^2,2at)

    3E question 4b

    I don't understand your question. However, this may help.

    If we take a curve which is double valued in y such as a circle the the formula is y=\pm \sqrt{r^2-x^2} which is not a function as it is double valued, i.e each value of x does not lead to only one value of y

    Introducing a parameter to give us  a=r \cos t, \; y=r \sin t gives us two single valued functions and by using values of t 0<t<=360 we can plot the function.

    The same is the case for a parabola which we swap a sqrt form (not a function) for the parameterised version of (say) x=at^2, y=at

    This enables us to find proper functions in t for the gradient etc using the chain rule.

    Does that answer in any way what you are asking?

    Soory, forgot to address the specific question. By eliminating t we end up with a cartesian form with y^2 in it. which we root out to find the form y=f(x) (the cartesian form) which is not as useful in a mathematical sense but at least has the benefit of getting us a mark or two at FP1

    (Original post by Acrux)
    why do we substitute t values back into P(at^2,2at)

    3E question 4b
    Because it wants the co-ordinates, not the parameter. The coordinates depend on t, so to find the coordinates you plug t.
Write a reply…


Submit reply


Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. Oops, you need to agree to our Ts&Cs to register
  2. Slide to join now Processing…

Updated: April 26, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

What were/are your predicted grades?
Useful resources

Make your revision easier


Maths Forum posting guidelines

Not sure where to post? Read here first


How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.