Factorial Ratio for Interval of Convergence Calculation

In summary, the question is asking for the ratio (2n+1)!/(2n+3)! and how to calculate it for the interval of convergence. The solution involves using the factorial property n! = n*(n-1)! to simplify the expression, resulting in 1/(4n^2+10n+6). This shows that the ratio is equal to infinity when n=-1 or -1.5.
  • #1
queensu
3
0

Homework Statement


Hi! I need to find ratio (2n+1)!/(2n+3)! for interval of convergence calculation.

Homework Equations


5! = 1*2*3*4*5

The Attempt at a Solution



i have no idea where to start since i have never dealt with factorials before.. if you just show me some kind off factorial property i can use ill be able to figure it out. wikipedia didnt help.
 
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  • #2


5! = 5*4*3*2*1 and 4! = 4*3*2*1, so
5! = 5*4!
5! = 5*4*3!

n! = n*(n -1)!
n! = n*(n-1)*(n-2)!
and more generally, n! = n*(n-1)*(n-2)...3*2*1

See if you can break down (2n + 1)! and (2n + 3)! so you can cancel something.
 
  • #3


oh.. awesome thanks a lot.
after very long thing of expanding that i got 1/ (2n+3)
 
  • #4


Your answer is not quite right, and obtaining the correct one should not take much expanding. You only need to apply the identity n! = n*(n-1)*(n-2)! to the denominator.
 
  • #5


(2n+3)=(2n+3)*(2(n-1)+1)! = 2n+3)*(2n-2+3)! =(2n+3)(2n+1)! ||| (2n+1)! cancels and I am left with 1/(2n+3)
 
  • #6


You should have (2n+2) somewhere; looks like you factored out the 2 and then it got lost...
 
  • #7


queensu said:

Homework Statement


Hi! I need to find ratio (2n+1)!/(2n+3)! for interval of convergence calculation.

Homework Equations


5! = 1*2*3*4*5

The Attempt at a Solution



i have no idea where to start since i have never dealt with factorials before.. if you just show me some kind off factorial property i can use ill be able to figure it out. wikipedia didnt help.

I think it is 1/(4n^2+10n+6)
 
  • #8


Like Bohrok said,

5! = 5*4*3*2*1 and 4! = 4*3*2*1, so
5! = 5*4!
5! = 5*4*3!

Use this logic to simplify your question. :smile:
It would go like this:-

[tex]\frac{(2n+1)!}{(2n+3)(2n+2)(2n+1)!}[/tex]

Now cancel out (2n+1)! and you get:-

[tex]\frac{1}{(2n+3)(2n+2)}[/tex]

Done ! :wink:
 
  • #9


Pranav-Arora said:
Like Bohrok said,

5! = 5*4*3*2*1 and 4! = 4*3*2*1, so
5! = 5*4!
5! = 5*4*3!

Use this logic to simplify your question. :smile:
It would go like this:-

[tex]\frac{(2n+1)!}{(2n+3)(2n+2)(2n+1)!}[/tex]

Now cancel out (2n+1)! and you get:-

[tex]\frac{1}{(2n+3)(2n+2)}[/tex]

Done ! :wink:

Umm... that can be simplified to 1/(4n^2+10n+6). From this, we can see that when and only when n=-1 or -1.5, (2n+1)!/(2n+3)!=infinity
 
Last edited:
  • #10


What did queensu mean by "for interval of convergence calculation"?
 

Related to Factorial Ratio for Interval of Convergence Calculation

What is a factorial?

A factorial is a mathematical operation denoted by the exclamation mark (!) symbol. It is used to calculate the product of a number and all the positive integers below it. For example, 5! (read as "five factorial") is equal to 5 x 4 x 3 x 2 x 1 = 120.

How do I calculate factorials?

To calculate factorials, you can either use a calculator or write out the multiplication equation. For larger numbers, using a calculator is recommended. However, for smaller numbers, you can use the formula n! = n x (n-1) x (n-2) x ... x 1, where n is the number for which you are calculating the factorial.

What is the significance of factorials in mathematics?

Factorials have many applications in mathematics and other fields. They can be used to calculate the number of ways to arrange a set of objects, the number of possible outcomes in a probability experiment, and the number of possible combinations in a given scenario. They are also used in various mathematical formulas and equations.

What is the largest factorial that can be calculated?

The limit for calculating factorials depends on the precision of the calculator or computer being used. However, the largest factorial that can be calculated exactly is 170!, which is equal to approximately 7.25741562 × 10^306. Beyond this, the numbers become too large to be stored in most computing systems.

How are factorials related to permutations and combinations?

Factorials are closely related to permutations and combinations. Permutations are the number of ways to arrange a set of objects in a specific order, while combinations are the number of ways to select a subset of objects from a larger set without regard to order. Both permutations and combinations can be calculated using factorials in their formulas.

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