Hey there! Sign in to join this conversationNew here? Join for free

Question from C3 mock - how is it supposed to work? Watch

    • Thread Starter
    Offline

    1
    ReputationRep:
    My whole class just had its C3 mock exam, which didn't go well for us at all. As the teachers aren't allowed to go through the papers until February, could anyone help me and my class understand a question that none of us managed to understand?

    f(t) = ke^t where k is a constant with one real solution. Find k. (4 marks)

    Nobody in the entire class has a clue where to start, so any help would be appreciated.
    • Community Assistant
    Offline

    18
    ReputationRep:
    (Original post by ChrisWolff)
    My whole class just had its C3 mock exam, which didn't go well for us at all. As the teachers aren't allowed to go through the papers until February, could anyone help me and my class understand a question that none of us managed to understand?

    f(t) = ke^t where k is a constant with one real solution. Find k. (4 marks)

    Nobody in the entire class has a clue where to start, so any help would be appreciated.
    There would be one real root, so if a quadratic equation can be formed b^2-4ac=0.
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by NotNotBatman)
    There would be one real root, so if a quadratic equation can be formed b^2-4ac=0.
    Yeah, we just discussed that as a class, but no clue how it turns into a quadratic.
    • Community Assistant
    Offline

    18
    ReputationRep:
    (Original post by ChrisWolff)
    Yeah, we just discussed that as a class, but no clue how it turns into a quadratic.
    What was the full question?
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by NotNotBatman)
    What was the full question?
    That's all we were given.
    Offline

    3
    ReputationRep:
    (Original post by ChrisWolff)
    My whole class just had its C3 mock exam, which didn't go well for us at all. As the teachers aren't allowed to go through the papers until February, could anyone help me and my class understand a question that none of us managed to understand?

    f(t) = ke^t where k is a constant with one real solution. Find k. (4 marks)

    Nobody in the entire class has a clue where to start, so any help would be appreciated.
    Differentiate then differentiate again?
    Or take logs then réarrangé??
    This just seems like a question with a constant it's not over confusing?
    Natural logs cant be négative And remove The exponential term to get a straight Line graph
    • Community Assistant
    Offline

    18
    ReputationRep:
    (Original post by ChrisWolff)
    That's all we were given.
    That's not possible. I think I've found the question; in part a.) you're given f(x) = 3-2e^{-x} so f(t) = 3-2e^{-t} . Now solve for one real root.
    Offline

    16
    ReputationRep:
    (Original post by ChrisWolff)
    That's all we were given.
    I vaguely remember seeing this question before. That's not all the information you were given, there should be an f:x somewhere in the question too. Just replace the x with t and then you will have f(t) which you can then solve for k using discriminant
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by NotNotBatman)
    That's not possible. I think I've found the question; in part a.) you're given f(x) = 3-2e^{-x} so f(t) = 3-2e^{-t} . Now solve for one real root.
    Oh, thanks, that might have been it. I don't think I got as far as the next bit. What paper was that from, if that's alright? I'd love to have another go at it for peace of mind.
    • Community Assistant
    Offline

    18
    ReputationRep:
    (Original post by ChrisWolff)
    Oh, thanks, that might have been it. I don't think I got as far as the next bit. What paper was that from, if that's alright? I'd love to have another go at it for peace of mind.
    Jan 2014 IAL.
 
 
 
  • 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
    Will you be richer or poorer than your parents?
    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

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.