Differential calculus

Maths and statistics discussion, revision, exam and homework help.

Announcements Posted on
Please change your TSR password 23-05-2013
Enter our travel-writing competition for the chance to win a Nikon 1 J3 camera 20-05-2013
IMPORTANT: You must wait until midnight (morning exams)/4.30AM (afternoon exams) to discuss Edexcel exams and until 1pm/6pm the following day for STEP and IB exams. Please read before posting, including for rules for practical and oral exams. 28-04-2013
Search Thread
Advanced Search
Sign in to Reply
  1. jami74's Avatar
    1 11-05-2012  15:44
    • Exalted and Worshipped Member
    • Location: South
    Differential calculus
    I'm stuck with a function of a function?

    I think I use the chain rule dy/dx = dy/du X du/dx

    But I don't know what to do. Could someone explain it to me really simply please?
  2. ViralRiver's Avatar
    2 11-05-2012  15:48
    • Overlord in Training
    • Posts: 2,408
    Re: Differential calculus
    Say you have y = sin(4x).

    A variation of the chain rule is to let u = 4x, v = sin(u).

    dy/dx = dv/dx = dv/du \times du/dx = cos(u) \times 4 = 4cos(u) = 4cos(4x)

    Does that make sense?
  3. raheem94's Avatar
    3 11-05-2012  15:55
    • TSR Demigod
    • Posts: 5,512
    Re: Differential calculus
    (Original post by jami74)
    I'm stuck with a function of a function?

    I think I use the chain rule dy/dx = dy/du X du/dx

    But I don't know what to do. Could someone explain it to me really simply please?
    Its better that you give the question you are stuck on.
  4. jami74's Avatar
    4 11-05-2012  16:08
    • Exalted and Worshipped Member
    • Location: South
    Re: Differential calculus
    (Original post by ViralRiver)
    Say you have y = sin(4x).

    A variation of the chain rule is to let u = 4x, v = sin(u).

    dy/dx = dv/dx = dv/du \times du/dx = cos(u) \times 4 = 4cos(u) = 4cos(4x)

    Does that make sense?
    I'm looking at it very hard. If I keep looking it might make sense and then I can apply it to my question.


    (Original post by raheem94)
    Its better that you give the question you are stuck on.
    Thank-you. It is y=cos^2x

    So is u = cos^2?
  5. raheem94's Avatar
    5 11-05-2012  16:13
    • TSR Demigod
    • Posts: 5,512
    Re: Differential calculus
    (Original post by jami74)
    I'm looking at it very hard. If I keep looking it might make sense and then I can apply it to my question.




    Thank-you. It is y=cos^2x

    So is u = cos^2?
    y = cos^2x \\ u=cosx \\ y=u^2

    Now find \displaystyle \frac{dy}{du} \ \ and \ \ \frac{du}{dx} .

    At the end, use the chain rule, \displaystyle \frac{dy}{dx} = \frac{dy}{du} \times \frac{du}{dx}
  6. jami74's Avatar
    6 11-05-2012  20:30
    • Exalted and Worshipped Member
    • Location: South
    Re: Differential calculus
    (Original post by raheem94)
    y = cos^2x \\ u=cosx \\ y=u^2

    Now find \displaystyle \frac{dy}{du} \ \ and \ \ \frac{du}{dx} .

    At the end, use the chain rule, \displaystyle \frac{dy}{dx} = \frac{dy}{du} \times \frac{du}{dx}
    Thank-you.
Sign in to Reply
Search Thread
Advanced Search
Share this discussion:  
Useful resources

Articles:

Study Help rules and posting guidelinesStudy Help Member of the Month nominationsGuide to MathematicsMathematics resourcesMathematics websitesMathematics revision notes in the TSR wikiCambridge Assessment admissions tests (including STEP)How to use LaTeXCareers in Mathematics

Useful Dates:

Quick Link:

Unanswered Maths Threads

Groups associated with this forum:

View associated groups
Article updates
Moderators

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

This forum is moderated by:

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

Shortcuts

Get Started

TSR Group

Using TSR

Info

Connect with TSR

Reputation gems:
The Reputation gems seen here indicate how well reputed the user is, red gem indicate negative reputation and green indicates a good rep.
Post rating score:
These scores show if a post has been positively or negatively rated by our members.