Original subtitles

What's going on, ladies and gentlemen?

I hope you're feeling good and that you are ready for a recursion challenge.

And in this challenge we are going to write a function, if feeble, not your function and recursive

one that will get some and which represent the index of an element enfeeble not you serious.

And the function should return the associated value to these given.

And so write the recursive function that receives this parameter or some number n and this and will

represent the index of a given element in Fibonacci series.

So you find, you get your index and then you find a value.

Ian Fibonacci.

Serious.

And for result.

For those of you who is not familiar with what we will not you seriously is.

Let's take a look.

So basically the formula, the general formula for if you will not be serious, looks like this.

So the first element when An equals two zero, when the index is zero, the first element, the value

is going to be zero.

The next element for an equals, the one when the index equals to one, the value will be one.

And we can see it right here.

And then every next element in these feeble notches serious is going to be calculated as the sum of

the two previous elements.

So, for example, we know that the first element is zero.

Then we have one and then we have the of the F for an equals two.

Two.

Right.

We can see the formula if An is greater than one.

So F of two equals two.

F of one which is one plus F of zero, which is zero.

And it will give us a total of one.

And then also in the same way you find what will be the value for an equals two three, which is the

total of the value of F two plus the value of F one.

So if we take further loop, for example, the series will look like this.

So for index zero, for index zero will have the value of zero.

Right.

That's based on the formula here.

And for index one, when N equals two one.

Right.

This line is for the index for N when N equals two one, that the value is also going to be one.

And we can see it here.

And then we know that we found out that F of one is one and F of two will be equal to F one plus F zero.

So if one plus F zero will give us one plus zero, which is a total of one, that's basically the serious

Fibonacci.

And if we want to find out what will be F three or four, we just take the sum of the two previous value

for these given value that we want to find out.

So F of three equals two, F of two plus F of one.

And we know both of them, which is one and one.

And the total result will be two and four for.

We can see that it will be equals to F three plus F two.

And we know that it's just two plus one, which is a total of three.

And if we wanted to find out what will be F five, it will be just three plus two, which is five and

so on.

You got the idea how to find all the elements are in the feeble natsheh serious.

And what you have to do is to write a recursive function, a recursive Fibonacci function that will

get some n some index and you will find out and return the value and index N.

So if it will receive an index of three, if it will receive an equals two three.

Then the function is going to return to and if the function will receive N for example, five.

So the function will return five.

Right.

Because five for index five, the value is calculated by the sum of two and three.

So this result should not be done or calculated in an iterative approach, but rather it should be done

using a recursion.

So take your time, think of the solution and I'll see you in the Solutions video.

Good luck, guys.