Turn on thread page Beta
    • Thread Starter
    Offline

    0
    ReputationRep:
    Hiya,

    I've been doing a differentiation question and when I got the final answer, i've checked my answer many times but it doesn't match the book's answer at all, so i'm just wondering if you guys can help me see if i have done a mistake or the book is wrong.

    dy/dx = 3x/(2√(3x-2)) + √(3x-2)

    i simplified it to 9x-4/(2(3x-2))

    but the book says ((9x-4)√3x-2)/(2(3x-2)

    i don't know how they still have √3x-2 on top of the fraction..... =S

    sorry it's a bit messy..
    Offline

    1
    ReputationRep:
    Can you post your working? As far as I can see, the book's answer is correct.
    Offline

    17
    ReputationRep:
    (Original post by strwbry_short_cake)
    Hiya,

    I've been doing a differentiation question and when I got the final answer, i've checked my answer many times but it doesn't match the book's answer at all, so i'm just wondering if you guys can help me see if i have done a mistake or the book is wrong.

    dy/dx = 3x/(2√(3x-2)) + √(3x-2)

    i simplified it to 9x-4/(2(3x-2))

    but the book says ((9x-4)√3x-2)/(2(3x-2)

    i don't know how they still have √3x-2 on top of the fraction..... =S

    sorry it's a bit messy..
    The book is right. When you ADD fractions, you don't times the denominator, they become the original. Thats where you went wrong

    Ie:

     \frac{1}{x} + \frac {1}{x} = \frac {2}{x}
    • Thread Starter
    Offline

    0
    ReputationRep:
    alright, here's my working......(i've probably done something really stupid.... ><
    sorry it's so messy...i don't know how to input fractions here...

    1. 3x/(2√3x-2) + √3x-2
    2. 3x/(2√3x-2) + 2(3x-2)/(2√3x-2).........(times by 2√3x-2 to the second fraction)
    i got 2(3x-2) because doesn't a √ x √ cancels........(√3x-2)(√3x-2) = 3x-2?
    Offline

    15
    ReputationRep:
    To be honest, I got (9x-4)/2Root(3x-2) which is same as book afaik

    just get denominators the same and add.
    Offline

    1
    ReputationRep:
    (Original post by strwbry_short_cake)
    [OP]
    ...
    i simplified it to 9x-4/(2(3x-2))
    ...
    Did you mean this to be \frac{9x-4}{2\sqrt{3x-2}} ?
    If so, then multiply top and bottom by \sqrt{3x-2} and compare with the book.
    Offline

    14
    ReputationRep:
    (Original post by strwbry_short_cake)
    alright, here's my working......(i've probably done something really stupid.... ><
    sorry it's so messy...i don't know how to input fractions here...

    1. 3x/(2√3x-2) + √3x-2
    2. 3x/(2√3x-2) + 2(3x-2)/(2√3x-2).........(times by 2√3x-2 to the second fraction)
    i got 2(3x-2) because doesn't a √ x √ cancels........(√3x-2)(√3x-2) = 3x-2?
    • Thread Starter
    Offline

    0
    ReputationRep:
    ah i see what mistake i have made now...thanks guys ><

    so is it ok to leave it as 9x-4/(2√3x-2)? cos the answer in the book is ((9x-4)√3x-2)/2(3x-2)..
    is it not as tidy to leave a square root in the denominator?
    Offline

    1
    ReputationRep:
    (Original post by strwbry_short_cake)
    ah i see what mistake i have made now...thanks guys ><

    so is it ok to leave it as 9x-4/(2√3x-2)? cos the answer in the book is ((9x-4)√3x-2)/2(3x-2)..
    is it not as tidy to leave a square root in the denominator?
    Some books/people/syllabi don't like roots in the denominator. I can't really see the problem with them.
    Offline

    3
    ReputationRep:
    1/2 + 1/2 = 1, not 1/2
    Offline

    1
    ReputationRep:
    :confused:
    Offline

    1
    ReputationRep:
    *remembers why he stopped doing maths at GCSE
    Offline

    1
    ReputationRep:
    (Original post by Barton1)
    *remembers why he stopped doing maths at GCSE
    This is towards the low end of AS/high end of GCSE! Maths gets a lot more fun than this! :yes::nutcase:
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: January 14, 2010

University open days

  1. University of Bradford
    University-wide Postgraduate
    Wed, 25 Jul '18
  2. University of Buckingham
    Psychology Taster Tutorial Undergraduate
    Wed, 25 Jul '18
  3. Bournemouth University
    Clearing Campus Visit Undergraduate
    Wed, 1 Aug '18
Poll
How are you feeling in the run-up to Results Day 2018?
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

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.