Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    4
    ReputationRep:
    Solve the following equation, give irration answers in terms of surds.

    x^4 - 5x^2 + 4 = 0

    therefore

    t^2 - 5t + 4 = 0

    Factorised as

    (t - 1)(t - 4)

    Therefore

    t = 1 or 4

    x = t^2 so

    x = 1 or 16.. WRONG

    so now i try putting t^2 - 5t + 4 = 0 into the quadratic formula

    again, t is 1 OR 4

    ...

    The answer in the book is saying +/- 1 OR +/- 2 ???

    Help please???

    Thanks,
    Sean
    Offline

    0
    ReputationRep:
    t doesn't equal x^2
    x^2 equals t

    (hope this helps )
    • Community Assistant
    Offline

    20
    ReputationRep:
    Community Assistant
    x^2 = 1 or x^2 = 4

    You have squared. This is not the right thing to do to find x!

    Edit: I said t and meant x!
    Offline

    0
    ReputationRep:
    t = x^{2}

    So

    x = \sqrt{t}
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by Mr M)
    x^2 = 1 or x^2 = 4

    You have squared. This is not the right thing to do to find t!
    what is right then?
    • Community Assistant
    Offline

    20
    ReputationRep:
    Community Assistant
    (Original post by loopylouise)
    t doesn't equal x^2
    x^2 equals t

    (hope this helps )
    I know what you are trying to say but you haven't managed it!
    • Community Assistant
    Offline

    20
    ReputationRep:
    Community Assistant
    (Original post by Bleak Lemming)
    what is right then?
    What operation "reverses" squaring?
    Offline

    0
    ReputationRep:
    (Original post by Mr M)
    I know what you are trying to say but you haven't managed it!
    ...rats... ah well, other people said it better... I'm gonna get some cafine
    • Community Assistant
    Offline

    20
    ReputationRep:
    Community Assistant
    (Original post by StephenP91)
    t = x^{2}

    So

    x = \sqrt{t}
    Is there anything you would like to change about that last line?
    Offline

    0
    ReputationRep:
    (Original post by Mr M)
    Is there anything you would like to change about that last line?
    Besides plus or minus, but I have taken that as a given. That and I can't remember how to do it in LaTex.
    • Community Assistant
    Offline

    20
    ReputationRep:
    Community Assistant
    (Original post by StephenP91)
    Besides plus or minus, but I have taken that as a given.
    Why have you taken that as given?
    Offline

    0
    ReputationRep:
    (Original post by Mr M)
    Why have you taken that as given?
    Look what I have said. I could have just typed it, but writing on this stupid IPod is effort as it is.
    Offline

    0
    ReputationRep:
    oh just give him the answer. He'll learn better when he realizes what simple mistakes he has done:

    (x^2 - 1)(x^2 - 4)

    x^2 = 1, 4.
    x = root(1 and root(4 = +/- 1 and +/- 2
    • Community Assistant
    Offline

    20
    ReputationRep:
    Community Assistant
    (Original post by StephenP91)
    Look what I have said.
    Ah-ha.

    /pm in latex
    • Community Assistant
    Offline

    20
    ReputationRep:
    Community Assistant
    When solving equations of the form x^2 = k (where k is positive), about one quarter of AS students only find the positive solution.
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Has a teacher ever helped you cheat?
    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
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • 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.