# Sequence formula $a_{n}$=((last term) - (n-1)(common diff))

1. ### Lebombo

136
Calc 2 will require some basic knowledge of sequences and series. Since this topic has never been covered in any of my past math classes, I am currently learning about sequences and series from scratch. On youtube, I found a video that contains an explanation of the General Term of the Arithmetic Sequence formula. It also contains another form which does not exist in my Algebra Textbook:

$a_{n}$ = ((last term) - (n-1)(common diff))

However, I think the person providing the youtube explanation makes a mistake in notation, which is causing me some confusion. If he has written this portion of his presentation correctly, then I will have to go back and review my confusion. So if anyone has a moment, could you fact check the portion of the derivation of this formula at exactly 9:16 - 9:23

http://www.youtube.com/watch?v=dbuwvw91fFc&list=PL56BFE1A5A41BC8D6

To me it seems $$a_{n}- a_{n-1}$$ should equal d, not -d , so did he intend to write $$a_{n} - a_{n+1} = -d$$

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3. ### ArcanaNoir

757
Yes this is a mistake. I think he meant to have $a_n-a_{n+1}=-d$

I watched the video but I didn't listen to it because I'm in class.

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