The thing is I'm getting everything right when it comes to the binomial theorem stuff but I don't understand by looking at the formulae what it means?
Also, when I say ''how does 2! (2-n)! equal 2'' I am referring to when you have to work out n on your own. The question is, for example:
(n) (2) = 15
So I got:
n! / 2!(n-2)! = 15
which goes to
n(n-1) / 2 = 15
which you can then solve through to get n=6 for a positive integer. However I don't understand how the bottom lone goes to 2 in this case from 2!(n-2)!
The thing is I'm getting everything right when it comes to the binomial theorem stuff but I don't understand by looking at the formulae what it means?
Also, when I say ''how does 2! (2-n)! equal 2'' I am referring to when you have to work out n on your own. The question is, for example:
(n) (2) = 15
So I got:
n! / 2!(n-2)! = 15
which goes to
n(n-1) / 2 = 15
which you can then solve through to get n=6 for a positive integer. However I don't understand how the bottom lone goes to 2 in this case from 2!(n-2)!
What do you mean by looking at the formula? You mean this?
r=0∑n(rn)an−rbr As for algebraic long division, it is a pretty imperative skill at Advanced Higher. So get good at it, you'll need it for complex numbers and some calculus (usually integration) questions, if there's no other method you can find, that is.
I'd definitely suggest learning LaTeX if you're going to be posting in here, it makes it easier for everyone involved so we don't have to decipher what you mean. It's actually much easier than you'd think!
(2n)=152!(n−2)!n!=15
As for how that becomes what you said, it's really simple. 2! = 2, as to how the bottom seems to "switch" to the top is from an understanding of factorials.
n!=1×2×3×…×(n−2)×(n−1)×n and (n-2)! is what you've got on the bottom which is obviously...
(n−2)!=1×2×3×…×(n−3)×(n−2)
It's then as simple as terms cancelling out. If you set these series on top of each other in a fraction
(n−2)!n! (I'm ignoring the 2! for now, as it doesn't really effect anything in terms of cancelling out, if you want a more mathematical way of putting it, I'm taking 1/2 out as a factor of the fraction)
Then if we expand this above fraction we get:
1×2×3…(n−3)×(n−2)1×2×3…(n−2)×(n−1)×n
And as you can see, if we cancel out terms we end up left with:
1(n−1)×n which can be rewritten as n(n−1)
So once again for emphasis:
2!(n−2)!n!=2!n(n−1)=2n(n−1) and since 2! = 2...
Set that equal to 15 and solve for n. (solution in spoiler)
Spoiler
Edit: (I need to stop adding exclamation points for emphasis when I'm talking about factorials. So much confusion could be caused. )
Some members might be interested in the draft (i.e. this won't apply to you!) new course specifications for maths, mechanics and statistics. At this stage, there's not a huge amount of information - the wording suggests there are minor changes afoot in the 'pure' maths course, but more significantly that they're scrapping the 'maths for applied maths' unit and replacing it with mechanics- and statistics-specific units instead.
The thing is I'm getting everything right when it comes to the binomial theorem stuff but I don't understand by looking at the formulae what it means?
Also, when I say ''how does 2! (2-n)! equal 2'' I am referring to when you have to work out n on your own. The question is, for example:
(n) (2) = 15
So I got:
n! / 2!(n-2)! = 15
which goes to
n(n-1) / 2 = 15
which you can then solve through to get n=6 for a positive integer. However I don't understand how the bottom lone goes to 2 in this case from 2!(n-2)!
Good luck guys! Advanced Maths is so much more interesting than Higher. It's also not as difficult as everyone says. There is just soooooo much in the course. I would guess about double what there is in higher (based on my notes jitters from both levels). As long as you keep on top of things and don't let yoursel trail behind you should be ok.
Oh. Why does he do this? I was looking at the 2 binomial theorem proofs in my notes and it does something similar. Why do proofs require this step?
We haven't actually some these proofs yet I'm just curious.
To combine the two fractions together you need to get them to have the same denominator. In the two fractions, one part of the denominator is k! and (k-1)! respectively. To make them the same you multiply top and bottom of the (k-1)! fraction by k since k! = (k-1)!k. The other part of the denominator is (n - k)! and (n - k + 1)!. To make them the same you multiply top and bottom of the (n - k)! fraction by (n - k + 1), since (n - k)!(n - k + 1) = (n - k + 1)!.
So if the bottom numbers differ by one then it take 1 away from the bottom number of the lefthand side?
And what if they don't differ by 1?
No by k-1 and k it just shows that the bottom number on the left differ by 1, rather than you having to do anything with them. Say if you have 5C3 + 5C4, then n = 5 and k = 4 in this case, so you get 5C3 + 5C4 = (n+1)Ck = 6C4.
If they don't differ by 1 then this rule doesn't apply and you need to use other rules depending on the situation.
So if the bottom numbers differ by one then it take 1 away from the bottom number of the lefthand side?
And what if they don't differ by 1?
Like ukd said, you may be asked to provide a proof like that in your exam. So it's not enough to just know the rule. You really have to understand it, and it looks like you're thinking about the maths the wrong way. e.g. you're looking at the fraction and wondering why n! = n!k (it doesn't!), instead of looking at the entire fraction to see that ukd is only doing a bit of manipulation. He's multiplied the fraction by 1. kk. Expressed the fraction in a different, but equivalent, way. Sometimes if you want to turn one expression into another, like above with nC(k-1) +nCk = (n + 1)Ck it's helpful to look at what you want it to be in the end, and work your way backwards, that makes the manipulation easier. I did this all the time with my proofs. Stops you going off in the wrong direction.
You should never be singling out a single part of expressions like in the proof above, you have to look at the entire equation to see what's been done to it. Follow the logic line-by-line, rather than term-by-term. This is the fun part of maths, I think. Memorising rules was all fine and dandy at Higher, but you really have to understand everything now to get by at AH.
I struggled with that question when I was starting off AH, too. Don't worry about it, bud. I asked some bloody obvious questions in last year's thread!