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

Integration by Substitution

Announcements Posted on
Find the answers: Edexcel GCSE maths unofficial mark scheme 05-05-2016
  1. Offline


    I got parts a & b but there's something I want to ask in general but using this as an example. In part c) I have to do dx/du but how do I know when to do that? I'm sure it hasn't come up in all the papers but I tripped up on the question because I got up to :

    4/2 (b:a)[x^3(lnu)du] but didn't get past this stage till I went through it with Exam Solutions, can anyone tell me when to look out for it please
  2. Online

    You have

     \displaystyle \int x^3 \ln (x^2+2) \ dx

    and you need to change this to an integral du using the substitution \displaystyle u=x^2+2

    The way to change dx to du is to find du/dx:

     \displaystyle \frac{du}{dx} = 2x \implies dx = \frac{du}{2x}

    Now substutute everything in, remembering that x^2=u-2.

    Post your working if you're still stuck. Or post the specific part that confuses you.
  3. Offline

    You have to do dx/du (or similar) for every substitution. It is how you change the dx into a du.
  4. Offline

    Thank you both, I got it now

    I was getting confused before because I thought it was an additional step. One question though - when you're finding the area/volume of a curve using Integration and I know when they are parametric, you add a little bit after the integral of y^2 as in it'll dx/dt*dt or something?


Submit reply


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: June 19, 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

Edexcel GCSE maths answers

Check the unofficial mark scheme

What date is the EU referendum on?
Useful resources

Make your revision easier


Maths Forum posting guidelines

Not sure where to post? Read here first


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.