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# Expansion SO VERY VERY URGENT! + Watch

1. Hi guys,

its part of a binomial question, basically i've found the series but now being asked ' to use your series to find an approximate value for (0.31)^1/2
if it asked to 'substitue a suitable value' of of x...I'd know what to do.

How do i se the series?
Thanks!
2. (Original post by dream123)
Hi guys,

its part of a binomial question, basically i've found the series but now being asked ' to use your series to find an approximate value for (0.31)^1/2
if it asked to 'substitue a suitable value' of of x...I'd know what to do.

How do i se the series?
Thanks!
what were you asked to expand? what value of x makes your original expression in brackets = 0.31?
3. (Original post by gdunne42)
what were you asked to expand? what value of x makes your original expression in brackets = 0.31?
ok, so if i were asked to expand (1+bx) ^0.5
then the question is basically to do the follwoing:

1+bx = 0.31
(value of b from previous question)x = 0.31-1
etc

right?...or wrong?
4. (Original post by dream123)
ok, so if i were asked to expand (1+bx) ^0.5
then the question is basically to do the follwoing:

1+bx = 0.31
(value of b from previous question)x = 0.31-1
etc

right?...or wrong?
yep, and then substitute the value of x into your expansion
5. (Original post by gdunne42)
yep, and then substitute the value of x into your expansion
so, when you're asked to 'use the series' to find an approximate value then that means you do the above and SUB into the expansion?

BUT

if they ask to 'substitute a suitable value of x' then they just want to you find it but NOT out it in the series? right?
6. (Original post by dream123)
so, when you're asked to 'use the series' to find an approximate value then that means you do the above and SUB into the expansion?

BUT

if they ask to 'substitute a suitable value of x' then they just want to you find it but NOT out it in the series? right?
I could be wrong but in my experience exam questions like this will always want you to sub into the expansion to produce an approximation of something

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