A2 C4 maths help please explain question

Watch
BubbleBabby
Badges: 15
Rep:
?
#1
Report Thread starter 3 years ago
#1
https://madasmaths.com/archive/iygb_...apers/c4_d.pdf
On question 2 why do we use binomial expansion?
On question 1b why are the limits flipped when you take out a quarter?
the solutions are below
https://madasmaths.com/archive/iygb_..._solutions.pdf
0
reply
Radioactivedecay
Badges: 16
Rep:
?
#2
Report 3 years ago
#2
The limits are flipped because they get rid of the minus. When evaluating an integral you can flip the limits by taking the negative of the integral, essentially multiplying the whole thing by -1. They use binomial cuz thats essentially what the question is asking you to do. "Suffienctly small" means it has a limit, just like in a binomial expansion, eg:modx<2/3. so thats a hint to use binomial esoansion.
0
reply
BubbleBabby
Badges: 15
Rep:
?
#3
Report Thread starter 3 years ago
#3
(Original post by Radioactivedecay)
The limits are flipped because they get rid of the minus. When evaluating an integral you can flip the limits by taking the negative of the integral, essentially multiplying the whole thing by -1. They use binomial cuz thats essentially what the question is asking you to do. "Suffienctly small" means it has a limit, just like in a binomial expansion, eg:modx<2/3. so thats a hint to use binomial esoansion.
i see so binomial expansion is not only to expand without having to do a tonne of work its also to find the smallest possible value or a value to a limit! i get it thanks.
0
reply
HeadHoncho
Badges: 14
Rep:
?
#4
Report 3 years ago
#4
(Original post by BubbleBabby)
i see so binomial expansion is not only to expand without having to do a tonne of work its also to find the smallest possible value or a value to a limit! i get it thanks.
It’s to find a suitable estimate when x is small.

I get the feeling you don’t really understand C4 binomial expansion properly
0
reply
BubbleBabby
Badges: 15
Rep:
?
#5
Report Thread starter 3 years ago
#5
(Original post by HeadHoncho)
It’s to find a suitable estimate when x is small.

I get the feeling you don’t really understand C4 binomial expansion properly
i don't think i do i thought binomial expansion was to avoid pascals triangle but when i have to do it for things when the expansion does not the binomial expansion i don't understand that. Why is it when you expand that fraction manually and via binomial expansion you get 2 different answers surly you should get the same answer?
0
reply
HeadHoncho
Badges: 14
Rep:
?
#6
Report 3 years ago
#6
(Original post by BubbleBabby)
i don't think i do i thought binomial expansion was to avoid pascals triangle but when i have to do it for things when the expansion does not the binomial expansion i don't understand that. Why is it when you expand that fraction manually and via binomial expansion you get 2 different answers surly you should get the same answer?
Pascal’s triangle coefficients work only for positive integers as the series is finite (there is a fixed number of terms)

But when you use a fraction or negative number as your index (basically all of C4 expansions) you only expand it manually. It also is an infinite sequence because, if you think about it, when you subtract 1 from a fraction or negative, you never get to 0, therefore the numerator of the coefficient never gets to 0 for the series to stop. You’ll therefore stop the series at a reasonable place (usually at x^3 or x^4). You might want to look at exam solutions, a short vid that explains everything better
0
reply
BubbleBabby
Badges: 15
Rep:
?
#7
Report Thread starter 3 years ago
#7
(Original post by HeadHoncho)
Pascal’s triangle coefficients work only for positive integers as the series is finite (there is a fixed number of terms)

But when you use a fraction or negative number as your index (basically all of C4 expansions) you only expand it manually. It also is an infinite sequence because, if you think about it, when you subtract 1 from a fraction or negative, you never get to 0, therefore the numerator of the coefficient never gets to 0 for the series to stop. You’ll therefore stop the series at a reasonable place (usually at x^3 or x^4). You might want to look at exam solutions, a short vid that explains everything better
Thanks
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Poll: What factors affect your mental health most right now? Post-lockdown edition

Anxiousness about restrictions easing (43)
5.8%
Uncertainty around my education (84)
11.34%
Uncertainty around my future career prospects (79)
10.66%
Lack of purpose or motivation (94)
12.69%
Lack of support system (eg. teachers, counsellors, delays in care) (39)
5.26%
Impact lockdown had on physical health (42)
5.67%
Social worries (incl. loneliness/making friends) (80)
10.8%
Financial worries (50)
6.75%
Concern about myself or my loves ones getting/having been ill (32)
4.32%
Exposure to negative news/social media (46)
6.21%
Difficulty accessing real life entertainment (24)
3.24%
Lack of confidence in making big life decisions (71)
9.58%
Worry about missed opportunities during the pandemic (57)
7.69%

Watched Threads

View All
Latest
My Feed