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# C4 binomial question Watch

1. Find the first four terms of by substituting a suitable value of x, find an approximation to

I'm pretty sure I've done a question like this before from C2 but i can't remember how to determine a suitable x value. I tried making 1-3x =97 but this was wrong. Any help would be appreciated
2. Try 1-3x=97k for any suitable k

For example:

If k=1, 1-3x=97.

If k=1/10, 1-3x=9.7.

etc.
3. Remember x has to be between -1/3 and 1/3. Also remember that you can manipulate 0.97^(3/2) to get 97^(3/2) using laws of indicies.
4. (Original post by raiden95)
Find the first four terms of by substituting a suitable value of x, find an approximation to

I'm pretty sure I've done a question like this before from C2 but i can't remember how to determine a suitable x value. I tried making 1-3x =97 but this was wrong. Any help would be appreciated
5. It would be easier to equate the 1-3x to something more smaller. This is so that when you input it in to the binomial expansion it will make it that little bit easier.

try equating 1-3x to 0.97
6. (Original post by raiden95)
Find the first four terms of by substituting a suitable value of x, find an approximation to

I'm pretty sure I've done a question like this before from C2 but i can't remember how to determine a suitable x value. I tried making 1-3x =97 but this was wrong. Any help would be appreciated
I'm sure we had this question a couple of weeks ago!

remember you need -1<3x<1 for the infinite binomial expansion to be valid, so you'll need to set 1-3x = 97k as suggested by the other posters where k is some suitable value that will give you a convenient multiplier when raised to the power 3/2.
7. (Original post by davros)
I'm sure we had this question a couple of weeks ago!

remember you need -1<3x<1 for the infinite binomial expansion to be valid, so you'll need to set 1-3x = 97k as suggested by the other posters where k is some suitable value that will give you a convenient multiplier when raised to the power 3/2.
I put k =0.1 and got x=-2.9
Then i tried k=0.01 and got x=0.01
So its less than 1 now and i know it must be 0.01 but k isn't always the same as x, so i use the x not k right always when substituting?
8. (Original post by aznkid66)
Try 1-3x=97k for any suitable k

For example:

If k=1, 1-3x=97.

If k=1/10, 1-3x=9.7.

etc.
Is my method correct?
9. (Original post by raiden95)
Is my method correct?
You need to set 1-3x = 0.97 and adjust using the pointers that notnek has given above
10. (Original post by Indeterminate)
You need to set 1-3x = 97 and adjust using the pointers that notnek has given above
Can you look at post 7 please
11. (Original post by raiden95)
Can you look at post 7 please
notnek's post number 4 actually gives you a clue what to choose for x
12. (Original post by davros)
notnek's post number 4 actually gives you a clue what to choose for x
I thought if its less than 1 thats what i choose?

And to be honest i really don't understand it
13. (Original post by notnek)
I don't quite understand how this works or how i can use it to find x
14. (Original post by raiden95)
I don't quite understand how this works or how i can use it to find x
Can you approximate 0.97 to that power?
15. (Original post by raiden95)
I thought if its less than 1 thats what i choose?

And to be honest i really don't understand it
What value of x would give you 0.97 inside the bracket?

How does 0.97 relate to 97?

How does relate to ?
16. Wheres this question from??
17. (Original post by raiden95)
I don't quite understand how this works or how i can use it to find x
It works because:

18. (Original post by Mr M)
It works because:

Just to clarify, we chose 0.97 because its less than 1? Or is it always 2dp
19. (Original post by raiden95)
Just to clarify, we chose 0.97 because its less than 1? Or is it always 2dp
It gives a value of x that is in the range of values that the expansion is valid for
20. (Original post by raiden95)
Just to clarify, we chose 0.97 because its less than 1? Or is it always 2dp
You are trying to make equal to something. is sensible as this means .

Remember the binomial expansion of is only valid for so you need to choose x carefully.

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