C1 series question

Hello,

How would you do part (d) for question 6? Please could you also show the steps to how you got the answer (answer is 25).

https://917c8db4f385e20466384eff57d816b2bed188db.googledrive.com/host/0B1ZiqBksUHNYMVhvRUNrcWJ6LXM/June%202013%20(R)%20QP%20-%20C1%20Edexcel.pdf

Thank you :smile:

Reply 1

Neuth

19

Original post by Shanahey

Hello,

How would you do part (d) for question 6? Please could you also show the steps to how you got the answer (answer is 25).

https://917c8db4f385e20466384eff57d816b2bed188db.googledrive.com/host/0B1ZiqBksUHNYMVhvRUNrcWJ6LXM/June%202013%20(R)%20QP%20-%20C1%20Edexcel.pdf

Thank you :smile:

Where have you got so far? What have you tried? :smile:

Reply 2

raahimaziz

Original post by Shanahey

Hello,

How would you do part (d) for question 6? Please could you also show the steps to how you got the answer (answer is 25).

https://917c8db4f385e20466384eff57d816b2bed188db.googledrive.com/host/0B1ZiqBksUHNYMVhvRUNrcWJ6LXM/June%202013%20(R)%20QP%20-%20C1%20Edexcel.pdf

Thank you :smile:

Couldn't you just find the first and the last terms and then use the formula to find the sum? i.e. n/2(a+l)

Reply 3

Alevel2015.

OK it's about noticing a pattern if you work out k you should get it as 3/2. Substituting that into x2 you get the answer - 1/2. And Substituting that into x3 should = 1. Therefore the pattern is if the number is odd then x=1 and is even x= - 1/2. You can prove this by working out x4 and that should equal - 1/2.

You can now use 1/2n(a+l) to work out the answer as 25: 1/2*100(1+-1/2) = 25

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