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

    Right, question 7 for anyone that may for some unknown reason have the sheet, but for those that don't:

    The 7th term of an arithmetic sequence is -2 and the 12th term is 8
    i) Find the first term and the common difference.

    (I got this as being common difference: 2, and first term as -14. If i'm wrong, please correct me here!)

    ii) The sum of the terms is 364
    Find the number of terms in the sequence.

    This is when i'm seriously lost. I thought you needed to have the last term to figure out number of terms? Which I don't seem to have :confused:

    First of all, good luck for tomorrow! I'm sitting it too. It's a retake, I thought I understood series and sequences last year, but now I really do.

    Second off, your (i) is correct. For (ii), there are two formulae - one where you need the last term, another where you don't. Do you have your formula book in front of you? Quickly Google OCR MEI maths formula booklet, and go to page 2, it's the first one when you search for it I think. Do you remember the formula Sn = 1/2n(2a +[n-1]d)? That's the one you need. Put in the numbers you worked out from (i), make it equal to 364, solve the quadratic that pops out, and you get n = 28 or -14. Usually I wouldn't give you the answer, but since the exam is tomorrow this gives you a chance to work it out! If you still can't get it, I'll post up my working. Good luck!! x
    • Thread Starter

    Ahhh perfect! Thank you so much for your help!
    Hope the exam went well x
Have you ever experienced racism/sexism at uni?
Useful resources

Make your revision easier


Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here


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