Hey there! Sign in to join this conversationNew here? Join for free
Turn on thread page Beta
    • Thread Starter
    Offline

    2
    ReputationRep:
    The question asks to find the Volume generated when the region bounded by the curves y = 2x^2 and the line y= 3 - x^2 is rotated 180 degrees about the y-axis.

    I have no idea what limits to use or how to start since the region bounded crosses over the y-axis. I tried using integrating both between y=0 and y=3, and then take one away from each other but that came up with the wrong answer.

    Thanks in advance for any help!

    (correct answer is (3pi)/2 for reference)
    Offline

    20
    ReputationRep:
    you need to find where the curves intersect... this will help with the limits
    • Thread Starter
    Offline

    2
    ReputationRep:
    the curves intersect at (1,2) and (-1,2)

    but the curve region goes up to 3 along the y axis (y=3-x^2) , im not very sure at all how to go about it
    • Study Helper
    Offline

    15
    Study Helper
    (Original post by Mr. Ee)
    The question asks to find the Volume generated when the region bounded by the curves y = 2x^2 and the line y= 3 - x^2 is rotated 180 degrees about the y-axis.

    I have no idea what limits to use or how to start since the region bounded crosses over the y-axis. I tried using integrating both between y=0 and y=3, and then take one away from each other but that came up with the wrong answer.

    Thanks in advance for any help!

    (correct answer is (3pi)/2 for reference)
    So, your shape is bounded by two curves and rotated about the y-axis.

    Notice that from y=0 to 2, the boundary is 2x^2, and from y=2 to 3 the boundary is 3-x^2.

    So, you'll need to set up two integrals, one for each part of the shape.
    Attached Images
     
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by ghostwalker)
    So, your shape is bounded by two curves and rotated about the y-axis.

    Notice that from y=0 to 2, the boundary is 2x^2, and from y=2 to 3 the boundary is 3-x^2.

    So, you'll need to set up two integrals, one for each part of the shape.
    Thank you thats sorted it out

    much appreciated!
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: October 27, 2015
Poll
“Yanny” or “Laurel”
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.