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

How do you get d=8 from first 3 terms: p, 5p-8, 3p+8 (I worked out p=4) Watch

Announcements
    • Thread Starter
    Offline

    8
    ReputationRep:
    p, 5p-8, 3p+8 for first term, second term, 3rd term

    I can work out that p=4 by working out the difference between the sequences, but then when you are asked to work out the 40th term of the sequence, the mark scheme says that d=8 is implied.

    How do you get d=8 from that?

    I know p (or a) = 4, by working out the differences between the terms. HOwever, how do you work out that d=8? I see that second term is -8 and third term is +8 but why does it vary from -8 to +8? Doesn't the value before p (so 5p or 3p) affect the value of d?

    Please can somebody explain, it would be greatly appreciated.
    • Community Assistant
    Offline

    18
    ReputationRep:
    (Original post by blobbybill)
    p, 5p-8, 3p+8 for first term, second term, 3rd term

    I can work out that p=4 by working out the difference between the sequences, but then when you are asked to work out the 40th term of the sequence, the mark scheme says that d=8 is implied.

    How do you get d=8 from that?

    I know p (or a) = 4, by working out the differences between the terms. HOwever, how do you work out that d=8? I see that second term is -8 and third term is +8 but why does it vary from -8 to +8? Doesn't the value before p (so 5p or 3p) affect the value of d?

    Please can somebody explain, it would be greatly appreciated.
    Write the sequence, substituting p=4 and the common difference is obvious.
    • Very Important Poster
    Offline

    21
    ReputationRep:
    (Original post by blobbybill)
    p, 5p-8, 3p+8 for first term, second term, 3rd term

    I can work out that p=4 by working out the difference between the sequences, but then when you are asked to work out the 40th term of the sequence, the mark scheme says that d=8 is implied.

    How do you get d=8 from that?

    I know p (or a) = 4, by working out the differences between the terms. HOwever, how do you work out that d=8? I see that second term is -8 and third term is +8 but why does it vary from -8 to +8? Doesn't the value before p (so 5p or 3p) affect the value of d?

    Please can somebody explain, it would be greatly appreciated.
    The second term is not 8, nor is the third term -8. Compute them again (remember the p's in each term) then work out d.
    • Thread Starter
    Offline

    8
    ReputationRep:
    (Original post by SeanFM)
    The second term is not 8, nor is the third term -8. Compute them again (remember the p's in each term) then work out d.
    Sorry, I worded it wrong. I meant that in the second term, I can see a -8, and in the third term, within that term there is a +8.

    Can you help me please?
    • Very Important Poster
    Offline

    21
    ReputationRep:
    (Original post by blobbybill)
    Sorry, I worded it wrong. I meant that in the second term, I can see a -8, and in the third term, within that term there is a +8.

    Can you help me please?
    That doesn't mean that the difference between term 2 and 3 is 16 because 5p changes to 3p as well.

    You're overcomplicating it to find d, work out the difference between two terms, given that you know what p is.
 
 
 
  • 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
    Break up or unrequited love?
    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.