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

Differentiation, turning points q

Announcements Posted on
Talking about ISA/EMPA specifics is against our guidelines - read more here 28-04-2016
  1. Offline

    ReputationRep:
    11i) Differentiate y = x^3 + 3x and what does this tell you about the number of turning points on the curve?

    I've found dy/dx to be 3x^2 + 3 and the answer is that there are no turning points, I don't understand how the dy/dx shows that

    any help would be great, thanks!
  2. Offline

    ReputationRep:
    what value does dy/dx have at a turning point?

    can you make 3x^2+3= that value??
  3. Offline

    ReputationRep:
    (Original post by Magenta96)
    11i) Differentiate y = x^3 + 3x and what does this tell you about the number of turning points on the curve?

    I've found dy/dx to be 3x^2 + 3 and the answer is that there are no turning points, I don't understand how the dy/dx shows that

    any help would be great, thanks!
    dy/dx means the rate of change of y with respect to x, i.e. how much y changes if you change x.
    So it's the gradient/slope of the curve.

    So if dy/dx = 4, then for every increase in x of 1, y will increase by 4. Basically a ratio of y:x, although someone will strike me down for saying it!

    When a curve is at its minima/maxima, it's flat, i.e. the slope is 0, and so dy/dx = 0

    Since you showed that 3x^2 + 3 = dy/dx, then for there to be a turning point, 3x^2 + 3 = 0

    Try solving that equation and you'll realise that you need to do root(-1), which provides no solutions, ergo there is no minima/maxima.
  4. Offline

    ReputationRep:
    (Original post by The Polymath)
    dy/dx means the rate of change of y with respect to x, i.e. how much y changes if you change x.
    So it's the gradient/slope of the curve.

    So if dy/dx = 4, then for every increase in x of 1, y will increase by 4. Basically a ratio of y:x, although someone will strike me down for saying it!

    When a curve is at its minima/maxima, it's flat, i.e. the slope is 0, and so dy/dx = 0

    Since you showed that 3x^2 + 3 = dy/dx, then for there to be a turning point, 3x^2 + 3 = 0

    Try solving that equation and you'll realise that you need to do root(-1), which provides no solutions, ergo there is no minima/maxima.
    Oh okay thanks!

Reply

Submit reply

Register

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: February 12, 2013
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.

Today on TSR

How to predict exam questions

No crystal ball required

Poll
How will you be voting in the EU referendum?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read here first

Equations

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