00:01
From your s to write the recursive and the explicit formula for this given arithmetic sequence.
00:06
Now, with an arithmetic sequence to write the formulas, you need to know two things.
00:10
You need to know your first term, which in this problem is five.
00:15
So we can start that off with the recursive formula and just say our first term, because that's what a1 stands for, is five.
00:23
Now, the second piece of information you need is that a sub n -9 -1 stays there.
00:28
But you need to know what your common difference is.
00:31
That's what this d stands for in this formula.
00:33
Now, common difference means what am i adding or subtracting to get to those next terms? so five to get to three, we would be subtracting two or adding a negative two, however you want to look at that.
00:49
Three, same thing.
00:50
I would subtract two or add negative two to get to one.
00:54
And we're going to see that that pattern continues.
00:57
Now, since negative 2s are the same all way across the board, that becomes your common difference.
01:05
So you're going to plug in negative 2 for d.
01:08
So then we just say minus 2 after that a sub and minus 1...