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# How do you get d=8 from first 3 terms: p, 5p-8, 3p+8 (I worked out p=4)

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1. p, 5p-8, 3p+8 for first term, second term, 3rd term

I can work out that p=4 by working out the difference between the sequences, but then when you are asked to work out the 40th term of the sequence, the mark scheme says that d=8 is implied.

How do you get d=8 from that?

I know p (or a) = 4, by working out the differences between the terms. HOwever, how do you work out that d=8? I see that second term is -8 and third term is +8 but why does it vary from -8 to +8? Doesn't the value before p (so 5p or 3p) affect the value of d?

Please can somebody explain, it would be greatly appreciated.
2. (Original post by blobbybill)
p, 5p-8, 3p+8 for first term, second term, 3rd term

I can work out that p=4 by working out the difference between the sequences, but then when you are asked to work out the 40th term of the sequence, the mark scheme says that d=8 is implied.

How do you get d=8 from that?

I know p (or a) = 4, by working out the differences between the terms. HOwever, how do you work out that d=8? I see that second term is -8 and third term is +8 but why does it vary from -8 to +8? Doesn't the value before p (so 5p or 3p) affect the value of d?

Please can somebody explain, it would be greatly appreciated.
Write the sequence, substituting p=4 and the common difference is obvious.
3. (Original post by blobbybill)
p, 5p-8, 3p+8 for first term, second term, 3rd term

I can work out that p=4 by working out the difference between the sequences, but then when you are asked to work out the 40th term of the sequence, the mark scheme says that d=8 is implied.

How do you get d=8 from that?

I know p (or a) = 4, by working out the differences between the terms. HOwever, how do you work out that d=8? I see that second term is -8 and third term is +8 but why does it vary from -8 to +8? Doesn't the value before p (so 5p or 3p) affect the value of d?

Please can somebody explain, it would be greatly appreciated.
The second term is not 8, nor is the third term -8. Compute them again (remember the p's in each term) then work out d.
4. (Original post by SeanFM)
The second term is not 8, nor is the third term -8. Compute them again (remember the p's in each term) then work out d.
Sorry, I worded it wrong. I meant that in the second term, I can see a -8, and in the third term, within that term there is a +8.

5. (Original post by blobbybill)
Sorry, I worded it wrong. I meant that in the second term, I can see a -8, and in the third term, within that term there is a +8.

That doesn't mean that the difference between term 2 and 3 is 16 because 5p changes to 3p as well.

You're overcomplicating it to find d, work out the difference between two terms, given that you know what p is.

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