Turn on thread page Beta

Curved surface FP2 watch

Announcements
    • Thread Starter
    Offline

    20
    ReputationRep:
    http://filestore.aqa.org.uk/subjects...W-QP-JUN11.PDF

    Question 5.

    I'm sitting on S = 2πy∫√(1 +x^2/(x^2+8))

    And i'm struggling to get to what they want me to show.

    Help pls
    Offline

    22
    ReputationRep:
    (Original post by Bobjim12)
    http://filestore.aqa.org.uk/subjects...W-QP-JUN11.PDF

    Question 5.

    I'm sitting on S = 2πy∫√(1 +x^2/(x^2+8))

    And i'm struggling to get to what they want me to show.

    Help pls
    I'm very alarmed by the fact that you have the y outside the integral sign... correct version:

    \displaystyle 2\pi \int_0^6 \sqrt{x^2 + 8} \sqrt{\frac{x^2 + 8 + x^2}{x^2 + 8}} \, \mathrm{d}x = 2\pi \int_0^6 \sqrt{2(x^2 + 4)} \, \mathrm{d}x
    • Thread Starter
    Offline

    20
    ReputationRep:
    (Original post by Zacken)
    I'm very alarmed by the fact that you have the y outside the integral sign... correct version:

    \displaystyle 2\pi \int_0^6 \sqrt{x^2 + 8} \sqrt{\frac{x^2 + 8 + x^2}{x^2 + 8}} \, \mathrm{d}x = 2\pi \int_0^6 \sqrt{2(x^2 + 4)} \, \mathrm{d}x
    i can never tell when we can just ignore the minus root, in this case y has two values............ this makes me sad.
    Offline

    22
    ReputationRep:
    (Original post by Bobjim12)
    i can never tell when we can just ignore the minus root, in this case y has two values............ this makes me sad.
    It would have made no difference had you taken the negative root - you'd get a negative area from which (I hope) you'd take the absolute value of to get the positive answer anyway. But at A-Level, you're nearly always going to be taking the positive root without any justification.

    In either case - y is inside the integral!
    • Thread Starter
    Offline

    20
    ReputationRep:
    (Original post by Zacken)
    It would have made no difference had you taken the negative root - you'd get a negative area from which (I hope) you'd take the absolute value of to get the positive answer anyway. But at A-Level, you're nearly always going to be taking the positive root without any justification.

    In either case - y is inside the integral!
    My head hurts.

    ok ty
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: March 13, 2016

University open days

  • University of Warwick
    Undergraduate Open Days Undergraduate
    Sat, 20 Oct '18
  • University of Sheffield
    Undergraduate Open Days Undergraduate
    Sat, 20 Oct '18
  • Edge Hill University
    Faculty of Health and Social Care Undergraduate
    Sat, 20 Oct '18
Poll
Who is most responsible for your success at university
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

Equations

Best calculators for A level Maths

Tips on which model to get

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.