The Student Room Group

C1 Arithmetic sequences


Sorry you can't really see the question. Show that (6r-7)=n(3n-1)
I have worked out that a=-1 and d=6 now I don't know what to do?
Reply 1
Sigma is the sum of, so you need to find the sum of (6r-7) then put it in terms of n.
Reply 2
Original post by jadechapell

Sorry you can't really see the question. Show that (6r-7)=n(3n-1)
I have worked out that a=-1 and d=6 now I don't know what to do?

What's the formula for finding the sum of an arithmetic series?
Reply 3
Original post by notnek
What's the formula for finding the sum of an arithmetic series?


2a+(n-1)d?
Reply 4
Original post by jadechapell
2a+(n-1)d?

Nearly.

Sum = (n/2)[2a+(n-1)d]

Substitute for a and d.
Reply 5
Original post by notnek
Nearly.

Sum = (n/2)[2a+(n-1)d]

Substitute for a and d.


Yay I have the right answer. I'm not entirely sure how I got there but thank you!

Quick Reply

Latest