Core Maths 3: Differentiation using the quotient rule

Announcements Posted on
How helpful is our apprenticeship zone? Have your say with our short survey 02-12-2016
    • Thread Starter
    Offline

    2
    ReputationRep:
    Hi there

    Please could someone tell me if the below is correct;



    Many thanks
    Jackie
    Offline

    0
    ReputationRep:
    I haven't checked the algebra but how did you go from the fraction at the bottom left to the next stage ? The question doesn't give us x.
    Offline

    1
    ReputationRep:
    (Original post by jackie11)
    Hi there

    Please could someone tell me if the below is correct;

    Many thanks
    Jackie
    According to the question you should leave your answer as  \displaystyle \frac{dy}{dx}=\frac{x^2+2x-1}{x^2+2x+1}

    Why did you wrote  \displaystyle \frac{1+1-1}{1+1+1} \ ?
    Offline

    0
    ReputationRep:
    (Original post by raheem94)
    According to the question you should leave your answer as  \displaystyle \frac{dy}{dx}=\frac{x^2+2x-1}{x^2+2x+1}

    Why did you sub in x=1?
    He didn't sub in x=1 otherwise the top would be 1 + 2 - 1 = 2

    He could make into a proper fraction I guess.
    Offline

    1
    ReputationRep:
    (Original post by member910132)
    He didn't sub in x=1 otherwise the top would be 1 + 2 - 1 = 2

    He could make into a proper fraction I guess.
    Thanks for correcting me, do you understand what he was trying to do?

    This can easily be made into a proper fraction, but i don't think he was trying to do this.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by raheem94)
    According to the question you should leave your answer as  \displaystyle \frac{dy}{dx}=\frac{x^2+2x-1}{x^2+2x+1}

    Why did you sub in x=1?
    ok thankyou, no I just assumed that when you have the same thing on the top and bottom, i.e.

    10/10, it becomes 1/1

    So that's what I did for x^2/x^2 and 2x/2x
    Offline

    3
    ReputationRep:
    (Original post by jackie11)
    Hi there

    Please could someone tell me if the below is correct;



    Many thanks
    Jackie
    Jackie, Jackie, Jackie

    You CANNOT do that

    You CANNOT cancel the x^2 and then cancel the 2x's ... NO NO NO NO
    Offline

    1
    ReputationRep:
    (Original post by jackie11)
    ok thankyou, no I just assumed that when you have the same thing on the top and bottom, i.e.

    10/10, it becomes 1/1

    So that's what I did for x^2/x^2 and 2x/2x
    10/10 becomes 1/1 but here the top has -1 and the bottom has +1.

    If you want to simplify it, then you can do it in the following way,
     \displaystyle \frac{x^2+2x-1}{x^2+2x+1}=\frac{x^2+2x+1-1-1}{x^2+2x+1}=\frac{x^2+2x+1}{x^2  +2x+1}-\frac2{x^2+2x+1}= \\  1-\frac2{x^2+2x+1}
    Offline

    2
    ReputationRep:
    (Original post by jackie11)
    ok thankyou, no I just assumed that when you have the same thing on the top and bottom, i.e.

    10/10, it becomes 1/1

    So that's what I did for x^2/x^2 and 2x/2x
    No you can't do that. say if we have \dfrac{x+3}{x+5}, that ISN'T equal to \dfrac{1+3}{1+5}

    You can only simplify a fraction if the top and bottom are multiplied by the same factor, not 'added on' by the same amount.

    E.g. the above isn't allowed, but this is:

    \dfrac{x(x+3)}{x(x+5)} = \dfrac{1(x+3)}{1(x+5)}

    EDIT: I'm sure you probably do know this, and are just getting confused but hopefully the examples helped
    • Thread Starter
    Offline

    2
    ReputationRep:
    aww thank you all so much
 
 
 
Write a reply… 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: April 23, 2012
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
Poll
Would you rather have...?
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

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

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