00:01
Okay, we got a word problem here with some context, which i always like.
00:03
It makes me feel like there's a reason to why we're doing what we're doing.
00:06
So, the theater has 20 seats in the first row and then three more every single row back.
00:10
So 20, then 23, then 26, and so forth.
00:18
And instead of adding up 35 different numbers for the 35 rows, i'm actually going to write this in sigma notation and say, okay, our first number, or a1, our first term, i should say, is 20.
00:30
And then i need to add n minus 1 multiplied by 3.
00:36
All this says is the difference here, the common difference is 3.
00:39
3 is being added every time for n minus 1 times, where we start with n equals 1 and go up to the 35th row.
00:49
Now, this is going to save me a lot of time because when i plug it in like this, i know i can plug it into this formula here.
00:56
And so let me go ahead and plug in 35 for n for the 35 rows over 2 .3.
01:01
The very first term is 20.
01:04
And i guess we have to figure out the nth term, which isn't going to be that hard.
01:08
So let's go ahead and plug in 35 for n right here.
01:12
And 35 minus 1 is in parentheses.
01:16
Well, that's 34...