A-Level Maths: D1-28 Binomial Expansion: Two Trickier Binomial Expansions

[quentinsummers]

you're such a life saver! I think you're only one teaching this on youtube and you're doing it so well. I'm watching all your episodes on it.Also, this has to be one of the(if not, the) most boring thing to be covered in maths so far. I mean, really whats the point in even expanding this? Especially, since the range of validity is often so tiny?
But still, thanks again!

[avacyn]

Could you do a partial fractions with Binomial Expansion video?

[alexedwardshasanhakim]

Amazing teacher! Thank you so much...makes much more sense now

[johnsergie]

Good evening, sorry to bother you but I was wondering if you could help me with this question, it would be highly appreciated:
In the binomial expansion of (3-kx)^6, where k is the constant, the coefficient of x^3 is -4320. Calculate:
a)The value of k
b)The value of the coefficient of x^4 in the expansion

Thanks.

[henryhatton]

Is it not possible to do this using the year one method of writing it out as a list?

[Masowe.]

so its always better to do 4 terms then drop the 4th at the final answer than to go back it seems

[bobbygreen]

Could you do a video on using a binomial expansion to find an approximation when the x value given to substitute in, doesn't make the bracket = what the approximation is for please. Here's an example question of it (it is part b I am on about but I included the full question. I believe the question is from A2 Specimen Paper 1 Q2).

a) show that the binomial expansion of (3+5x)^0.5 is 2 + (5/4)x + kx^2

b) Use the expansion with x=1/10 to find an approximate value for sqrt (2)

The video's are brilliant thank you and I don't think you've done a video on this (correct me if I'm wrong!). It would be much appreciated cheers

[mariamelsergani]

Hi, I was wondering why you ignored the cubic term at 3:19 but then ended up having a cubic term in the final answer?