A Level maths question

https://www.quora.com/profile/Bravewarrior/p-166721296
Here is the question I'm stuck on. In the mark scheme they've used the formula for sum to n terms of an arithmetic series. Can someone please tell me why they didn't use the geometric one as at first glance it seemed like a geometric series to me

Thanks!

Reply 1

madzzzzina

You’re finding the sum of the terms between when n=1 and when n=11.

With these questions, try to substitute n for the first few terms.

So, start off with substituting n=1. What do you get in terms of p? Then substitute n=2, then n=3, then n=4. What do you get? Is there another way of writing each term? What’s the difference between each term - is it addition/subtraction or a multiplication/division?

Also, may I ask, where are you getting these questions from? I’d like to try them as well lol.

(edited 7 months ago)

Reply 2

pigeonwarrior

Original post by madzzzzina

You’re finding the sum of the terms between when n=1 and when n=11.
With these questions, try to substitute n for the first few terms.
So, start off with substituting n=1. What do you get in terms of p? Then substitute n=2, then n=3, then n=4. What do you get? Is there another way of writing each term? What’s the difference between each term - is it addition/subtraction or a multiplication/division?
Also, may I ask, where are you getting these questions from? I’d like to try them as well lol.