Turn on thread page Beta

Help with parametric equations watch

Announcements
    • Thread Starter
    Offline

    8
    ReputationRep:
    A curve is defined parametrically by x = (t^2 + 1) , y = t^3
    Find (dy)/(dx) when t = 2

    The chain rule: (dy/dx) = (dy/dt) x (dt/dx)
    My calculation says that x = 5, y = 8
    so (dy/dx) must equal 8/5 but the answet given is 3.
    Can anybody help me?
    Offline

    12
    ReputationRep:
    you calculated y/x not (dy/dt) x (dt/dx)

    Find dy/dx in terms of t and then replace
    • Thread Starter
    Offline

    8
    ReputationRep:
    But (to me) i see dy/dx and just see that cancelling down into y/x? Finding in terms of t isnt helping me
    Posted on the TSR App. Download from Apple or Google Play
    Offline

    12
    ReputationRep:
    (Original post by pontifexmaximus)
    But (to me) i see dy/dx and just see that cancelling down into y/x? Finding in terms of t isnt helping me
    d/dx is an operator. You cannot cancel d from it to get 1/x

    d/dx means differentiate wrt x.

    d/dx (y) means differentiate y wrt x. This is written as dy/dx. You cannot simplify this to y/x.

    Finding dy/dx in terms of t is helping you as you just replace t = 2 and get the gradient

    Use chain rule dy/dx = dy/dt divided by dx/dt
    • Thread Starter
    Offline

    8
    ReputationRep:
    ok well its clear to me that i dont have a clue lol my course book has just dropped this thing on me without teaching me any of this stuff beforehand lmao
    thanks for the help
    Posted on the TSR App. Download from Apple or Google Play
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: December 10, 2018

University open days

  • University of East Anglia
    All Departments Open 13:00-17:00. Find out more about our diverse range of subject areas and career progression in the Arts & Humanities, Social Sciences, Medicine & Health Sciences, and the Sciences. Postgraduate
    Wed, 30 Jan '19
  • Aston University
    Postgraduate Open Day Postgraduate
    Wed, 30 Jan '19
  • Solent University
    Careers in maritime Undergraduate
    Sat, 2 Feb '19
Poll
Brexit: Given the chance now, would you vote leave or remain?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Equations

Best calculators for A level Maths

Tips on which model to get

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

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

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