Direct formula derived from recursive formula

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In summary, the conversation is about finding a direct formula for a recursive formula where the base is not given. The difference between terms is 2n, but the person is unsure how to proceed. They are advised to use the explicit formula for the sum of consecutive numbers, and then adjust for the initial term being different.
  • #1
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Homework Statement


I have a recursive formula and I'm trying to find a direct formula.

Homework Equations


The recursive formula: T(n) = T(n-2) + n^2

No base is given. The question says "Assume that T(n) is constant for n <- 2

The Attempt at a Solution


T(1) = 0
difference: 4
T(2) = 4
difference: 6
T(3) = 10
difference: 8
T(4) = 18
difference: 10
T(5) = 28

So the difference is 2n, but then I get stuck and don't know how to go further and get a direct formula.
 
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  • #2
Do you know the explicit formula for [tex]1 + 2 + \dots + n[/tex]? It will help you solve this problem, and it's something you should know anyway. (Hint: fold the sequence in the middle.)
 
  • #3
The sum from k=0 to n of s+kv = (n+1) s + 1/2 n(n+1)v

But I don't know what to do because the difference doesn't start with 2
 
  • #4
Imagine it did, then correct for the problem afterward!
 

1. What is a direct formula derived from a recursive formula?

A direct formula derived from a recursive formula is a mathematical expression that allows you to directly calculate a value in a sequence, without having to go through each step of the recursive process. It is derived by analyzing the pattern in the recursive formula and finding a way to express it in a simpler, more direct form.

2. Why is it important to have a direct formula for a recursive sequence?

Having a direct formula for a recursive sequence can save time and effort in calculating values, especially for larger numbers. It also allows for easier analysis and understanding of the sequence, as well as the ability to predict future values.

3. How do you find the direct formula for a recursive sequence?

The process of finding a direct formula for a recursive sequence involves analyzing the pattern in the recursive formula and finding a way to express it in a simpler, more direct form. This can be done by looking for common terms and using algebraic manipulation to simplify the expression.

4. Can a direct formula be used for any type of recursive sequence?

Not all recursive sequences have a direct formula, as some may have patterns that are too complex to express in a simple formula. However, for many common types of recursive sequences, such as arithmetic and geometric sequences, a direct formula can be derived.

5. How accurate is a direct formula compared to a recursive formula?

A direct formula and a recursive formula should give the same results when calculating values in a sequence. However, a direct formula may be more prone to rounding errors due to the use of more operations. It is important to check for accuracy when using a direct formula for a recursive sequence.

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