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# fp1 linear laws Watch

1. This is the question I'm trying to do
-----------------------------------------------------------
in an experiment these results are obtained

x = 1 2 3 4 5
y= 9 23.1 60.9 135 257

it is believed that a formula exists such as y = ax^3 + b connects y and x. Test to find if the results do satisfy such a formula, and find the values of a and b
----------------------------------------------

So I cubed the x values and then did a plot on graph paper. This wasn't very practical so I did something that I'd learnt in S1 about regression lines. I used a calculator and used the y = a + bx facility. I got y = -3.5 +0.5x. I suppose that's 0.5 x^3.

The answer in the book is a= -1/3 and b = 7/2

What am I not understanding?

Thanks
2. (Original post by maggiehodgson)
...
Both answers are incorrect. Consider where .
3. (Original post by maggiehodgson)
This is the question I'm trying to do
-----------------------------------------------------------
in an experiment these results are obtained

x = 1 2 3 4 5
y= 9 23.1 60.9 135 257

it is believed that a formula exists such as y = ax^3 + b connects y and x. Test to find if the results do satisfy such a formula, and find the values of a and b
----------------------------------------------

So I cubed the x values and then did a plot on graph paper. This wasn't very practical so I did something that I'd learnt in S1 about regression lines. I used a calculator and used the y = a + bx facility. I got y = -3.5 +0.5x. I suppose that's 0.5 x^3.

The answer in the book is a= -1/3 and b = 7/2

What am I not understanding?

Thanks
The dat almost exactly fit
4. (Original post by maggiehodgson)
I did something that I'd learnt in S1 about regression lines. I used a calculator and used the y = a + bx facility. I got y = -3.5 +0.5x. I suppose that's 0.5 x^3.
This would have worked but you have entered the y values in the x column and x^3 values in the y column.

Try it again and you will see that as brianeverit says is a very good fit.
5. Thank you all.

I made 2 errors. Firstly, I looked at the wrong set of answers in the book. Secondly, I did indeed enter the y values in the x column and the x^3 values in the y column.

It all works now.
6. (Original post by maggiehodgson)
Thank you all.

I made 2 errors. Firstly, I looked at the wrong set of answers in the book. Secondly, I did indeed enter the y values in the x column and the x^3 values in the y column.

It all works now.
What are FP1 linear laws? I've looked over Fp1 vidos+ spec and have found nothing of the sort.
7. (Original post by MathMeister)
What are FP1 linear laws? I've looked over Fp1 vidos+ spec and have found nothing of the sort.
try looking in the AQA FP1 specification.
8. (Original post by MathMeister)
What are FP1 linear laws? I've looked over Fp1 vidos+ spec and have found nothing of the sort.
newton interpolation formula or lagrange

Posted from TSR Mobile
9. (Original post by MathMeister)
What are FP1 linear laws? I've looked over Fp1 vidos+ spec and have found nothing of the sort.

I'm doing AQA. Don't know if it's in your syllabus. I'm using a book called Advanced Maths for AQA Further Pure 1 and it's the last chapter. I've been looking at past papers and on the 4 I've looked at there is a question on it. For example June 07 question 5.

Hope this helps. Perhaps you've done it but call it something else. I'm not in a school so I call it what the book calls it.

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