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### History and Feedback

#### Checkpoint description

Describe what's changed since the last checkpoint.

#### Christian Lawson-Perfect2 years, 3 months ago

Gave some feedback: Ready to use

#### Christian Lawson-Perfect2 years, 3 months ago

Saved a checkpoint:

I've vastly rewritten the advice, and given the variables sensible names.

It would be good to have another version of this question where you fill in the table first.

Published this.

#### Aiden McCall2 years, 4 months ago

Saved a checkpoint:

I have edited the advice. I think the spacing/positioning could be done better but am not sure how to do this with the tables so they don't stretch when you move each part.

#### Aiden McCall2 years, 4 months ago

Saved a checkpoint:

The advice in this question is very hard to follow. I have an alternative method and am going to change the advice. In case my method is not preferred or wants to be reverted I have made a checkpoint here.

#### Hannah Aldous2 years, 4 months ago

Gave some feedback: Needs to be tested

#### Hannah Aldous2 years, 4 months ago

Gave some feedback: Has some problems

#### Hannah Aldous2 years, 4 months ago

Gave some feedback: Needs to be tested

#### Christian Lawson-Perfect2 years, 4 months ago

Also, note that I used "first differences" and "second differences" - I thnk Lauren also spotted that it's tricky to keep track of all the differences floating about.

#### Christian Lawson-Perfect2 years, 4 months ago

Gave some feedback: Has some problems

#### Christian Lawson-Perfect2 years, 4 months ago

Saved a checkpoint:

The layout of the advice is very hard to follow.

I would work this out by drawing up a table with rows for $n$, $a_n$, and first and second differences.

For example,

 $n$ 1 2 3 4 $a_n$ 15 22 33 48 First differences 7 11 15 Second differences 4 4

Because the second difference is $4$, I know that the coefficient of $x^2$ is $4/2 = 2$.

Then I can add a row for $a_n - 2n^2 = bn+c$:

 $n$ 1 2 3 4 $a_n$ 15 22 33 48 $2n^2$ 2 8 18 32 $a_n-2n^2$ 13 14 15 16

So $bn+c = n+12$, and the formula for the whole sequence is $a_n = 2n^2+n+12$.

Sometimes, a good layout can save a lot of verbiage!

#### Hannah Aldous2 years, 4 months ago

Gave some feedback: Needs to be tested

#### Lauren Richards2 years, 4 months ago

Gave some feedback: Has some problems

#### Lauren Richards2 years, 4 months ago

• So after you have found the difference between the sequential terms, and then found the difference between the differences, which you found in the question I did to be 8, it is not clear how you would decide to start the nth term off as 8/2n^2. I think you need to add in a line explaining your reasoning for this.
• I don't think the first sentence reads very well. Maybe something more like "We first need to calculate the differences between the terms in the sequence.". and then for the second bit of writing "We can then calculate the differences of the term differences." I totally get that that is quite hard to word without being confusing.
• I think "original sequence" should probably be capitalised.
• In the advice, the second bit of writing that finishes with the word differences, is missing a full stop. You're also missing a comma at the end of "difference" near the end of the advice but I think this sentence should be re-worded anyway as it starts with "If", but then doesn't really end it like you would expect. I think it should be something like "We should first find the common difference.".
• No fault of yours but it gets a little confusing with the amount of differences being mentioned, and I think when you refer to the "sequence of differences" you should have sequence of differences in brackets when you first make it to make it clear when you next refer to it.
• I think differences sequence should be capitalised.
• At the end, you're calculating the difference between 2n and the sequence of differences but you haven't done that in the same way as you have done earlier in the question advice and I think you probably should do.
• One time I did the question, it said "Then we can find the difference between 1n and our sequence of differences" so I think you should make sure it just states "n" in this case.
• I think this is a good question, and tricky to make clear!

#### Hannah Aldous2 years, 4 months ago

Gave some feedback: Needs to be tested

#### Vicky Hall2 years, 4 months ago

Gave some feedback: Has some problems

#### Vicky Hall2 years, 4 months ago

I would reword the question to say 'Find the formula for the $n$th term of the quadratic sequence'.

The advice is good but think the last part, where you find the constant, would look better if it were laid out like the previous part, so you show the student what the sequence $3n^2+3n$ looks like compared to the original sequence. You also need to remove the reference to part b).

#### Hannah Aldous2 years, 4 months ago

Gave some feedback: Needs to be tested

#### Hannah Aldous2 years, 5 months ago

Created this as a copy of Compute the partial sum of an arithmetic sequence.
Arithmetic sequences in an ice cream shop Ready to use Hannah Aldous 20/11/2019 14:36
Compute the partial sum of an arithmetic sequence Ready to use Hannah Aldous 20/11/2019 14:36
Finding the $n^{\text{th}}$ Term of a Quadratic Sequence Ready to use Hannah Aldous 20/11/2019 14:39
Identifying different types of sequences Ready to use Hannah Aldous 20/11/2019 14:40
Finding the formula for the $n^{\text{th}}$ term of linear sequences Ready to use Hannah Aldous 20/11/2019 14:39
Partial sum of an arithmetic sequence - birthday money Ready to use Hannah Aldous 20/11/2019 14:41
Find common difference in arithmetic sequences with gaps Ready to use Christian Lawson-Perfect 20/11/2019 14:39
Fill in the gaps in an arithmetic sequence Ready to use Christian Lawson-Perfect 20/11/2019 14:39
Write down and apply the formula for an arithmetic sequence. Ready to use Christian Lawson-Perfect 20/11/2019 14:46
Finding the Formula for the $n^{\text{th}}$ Term of Linear Sequences draft Chris Graham 20/07/2017 15:08
Inbbavathie's copy of Find common difference in arithmetic sequences with gaps draft Inbbavathie Ravi 24/07/2017 03:48
Find a particular term of a sequence using the given formula Ready to use Christian Lawson-Perfect 20/11/2019 14:38
Johan's copy of Write down and apply the formula for an arithmetic sequence. Has some problems Johan Maertens 02/08/2017 17:51
Finding the formula for the $n^{\text{th}}$ term of linear sequences draft steve kilgallon 19/11/2017 08:09
Compute the partial sum of an arithmetic sequence draft steve kilgallon 19/11/2017 08:11
Identifying different types of sequences draft Luis Hernandez 31/12/2018 01:38
Calcular la suma parcial de una sucesión aritmética Ready to use Luis Hernandez 14/01/2019 17:37
Identificando diferentes tipos de secuencias Ready to use Luis Hernandez 14/01/2019 13:19
Suma parcial de una secuencia aritmética - Cumpleaños Ready to use Luis Hernandez 14/01/2019 19:01
Encontrar la diferencia común en una Secuencia Aritmética Ready to use Luis Hernandez 14/01/2019 17:40
Encuentra un término particular de una secuencia usando la fórmula dada Ready to use Luis Hernandez 14/01/2019 17:48
Encontrar la fórmula para el término $n^{\text {th}}$ de una secuencia lineal Ready to use Luis Hernandez 14/01/2019 19:29
Simon's copy of Write down and apply the formula for an arithmetic sequence. draft Simon Thomas 25/02/2019 10:20
Simon's copy of Find common difference in arithmetic sequences with gaps draft Simon Thomas 25/02/2019 10:24
Simon's copy of Finding the formula for the $n^{\text{th}}$ term of linear sequences draft Simon Thomas 25/02/2019 10:30
Identifying different types of sequences draft Xiaodan Leng 10/07/2019 21:48
Write down and apply the formula for an arithmetic sequence. draft Xiaodan Leng 11/07/2019 01:48
Fill in the gaps in an arithmetic sequence draft Xiaodan Leng 11/07/2019 01:48
Find common difference in arithmetic sequences with gaps draft Xiaodan Leng 11/07/2019 01:49
Compute the partial sum of an arithmetic sequence draft Xiaodan Leng 11/07/2019 01:51
Partial sum of an arithmetic sequence - birthday money draft Xiaodan Leng 11/07/2019 01:54
Arithmetic sequences in an ice cream shop draft Xiaodan Leng 11/07/2019 01:55
Finding the formula for the $n^{\text{th}}$ term of linear sequences draft Xiaodan Leng 11/07/2019 01:55
Find a particular term of a sequence using the given formula draft Xiaodan Leng 11/07/2019 01:56
Finding the $n^{\text{th}}$ Term of a Quadratic Sequence draft Xiaodan Leng 11/07/2019 01:57
Paul's copy of Inbbavathie's copy of Find common difference in arithmetic sequences with gaps draft Paul Verheyen 05/10/2019 09:39

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