00:01
So in this question, we want to find the sum of the arithmetic series.
00:05
We want to find the 60 -second partial sum of what looks like this guy here.
00:12
Now, enumerate, it's better to take pictures than to cut and pace because oftentimes it just doesn't come through very well.
00:21
So taking pictures is going to be a better approach for you.
00:24
But i think what we have here is negative 23 plus negative 21.
00:33
Plus negative 20 plus dot dot dot.
00:38
So what do we know about the sums of an arithmetic series? the formula for a partial sum of an arithmetic series is s sub n equals n times the quantity of a1 plus an all being divided by two, where n is the number of terms being added together.
01:03
So here i'm going to want s62, my 62 partial sum.
01:11
What is that? it's 62 times the quantity of a1 plus a62, all being divided by 2.
01:22
Now, a1 is my first term.
01:25
It's negative 23.
01:28
But what about a62? well, in an arithmetic sequence, you have a formula for a sub -n.
01:37
A sub n is equal to a1 plus the quantity of n minus 1 times d.
01:47
So if i want a62, that's a1.
01:53
My a1 is negative 23, plus the quantity of n, my n here again is 62 minus 1 times my d...