# Recursive relationship definition math

### Recurrence relation - Wikipedia

In fact, a recurrence relation uses recursion to define a sequence. This sequence is built in such a way that each term is defined as a. foundations of mathematics: Recursive definitions Through this relationship all things that are values of “x is human” are selected by a back reference. The terms of a recursive sequences can be denoted symbolically in a number of of mathematics led to the formal definition of so-called recursive functions.

So let's see what happens. When k is 1, we get 1. When k is 2, we get 4. When k is 3, we get 7. When k is 3, we added 3 twice.

Let me make it clear. So this was a plus 3. This right over here was a plus 3. This right over here is a plus 3. So whatever k is, we started at 1. And we added 3 one less than the k term times. So we could say that this is going to be equal to 1 plus k minus 1 times 3, or maybe I should write 3 times k minus same thing.

And you can verify that this works. If k is equal to 1, you're going to get 1 minus 1 is 0. And so a sub 1 is going to be 1. If k is equal to 2, you're going to have 1 plus 3, which is 4. If k is equal to 3, you get 3 times 2 plus 1 is 7. So it works out. So this is one way to explicitly define our sequence with kind of this function notation.

### Sequences intro | Algebra (video) | Khan Academy

I want to make it clear-- I have essentially defined a function here. If I wanted a more traditional function notation, I could have written a of k, where k is the term that I care about. This is essentially a function, where an allowable input, the domain, is restricted to positive integers.

Now, how would I denote this business right over here?

Well, I could say that this is equal to-- and people tend to use a. But I could use the notation b sub k or anything else.

## Math Insight

But I'll do a again-- a sub k. And here, we're going from our first term-- so this is a sub 1, this is a sub all the way to infinity. Or we could define it-- if we wanted to define it explicitly as a function-- we could write this sequence as a sub k, where k starts at the first term and goes to infinity, with a sub k is equaling-- so we're starting at 3.

And we are adding 4 one less time. For the second term, we added 4 once. For the third term, we add 4 twice. For the fourth term, we add 4 three times. So we're adding 4 one less than the term that we're at.

## Recursive Sequence

So it's going to be plus 4 times k minus 1. So this is another way of defining this infinite sequence. Now, in both of these cases, I defined it as an explicit function. So this right over here is explicit. That's not an attractive color. Let me write this in. This is an explicit function. And so you might say, well, what's another way of defining these functions?

Well, we can also define it, especially something like an arithmetic sequence, we can also define it recursively. And I want to be clear-- not every sequence can be defined as either an explicit function like this, or as a recursive function.

But many can, including this, which is an arithmetic sequence, where we keep adding the same quantity over and over again.

So how would we do that? Well, we could also-- another way of defining this first sequence, we could say a sub k, starting at k equals 1 and going to 4 with. And when you define a sequence recursively, you want to define what your first term is, with a sub 1 equaling 1. You can define every other term in terms of the term before it. And so then we could write a sub k is equal to the previous term.

So this is a sub k minus 1. So a given term is equal to the previous term.

Let me make it clear-- this is the previous term, plus-- in this case, we're adding 3 every time. Most recursive functions will give you the beginning value or values that are needed to fully calculate the sequence. Without these beginning values, there is no way to determine what the real values for each term should be.

Expanding It Now, let's look at how you work with this recursive formula. Recursive functions are usually sequences. It gives you the formula to find the next term, if you know the previous terms. So, to calculate your terms from a recursive formula, you begin by writing out your beginning numbers. So with the beginning recursive formula that you saw, the first two terms in the sequence are 1 and 1.

Now, to find the third number in the sequence, when n is 3, you calculate your function for a sub 3.

### Recursive function | mathematics | vifleem.info

The Third Term This function is telling you that the third term in the sequence is equal to the second term plus the first term. The fourth term, according to the function, is this: The Fourth Term You begin to see the pattern here. Each term is the sum of the previous two terms.