00:01
So we're being asked to find the sum of this arithmetic series.
00:05
Well, we know that a sub 1 is equal to 2.
00:08
That's the first term.
00:09
We know d because to get from one term to the next, we simply add 2.
00:14
So d is equal to 2.
00:16
And we know that our last term is 70.
00:18
So a sub n is equal to 70.
00:21
So what we need to find is we need to find our end value.
00:24
So to do this, we're going to use our general formula to find any term in arithmetic sequence.
00:31
Which remember is the formula a sub n equals a sub 1 plus the quantity of n minus 1 times d.
00:39
So let's substitute the values that we have.
00:41
So we're going to have 70 is equal to 2 plus the quantity of n minus 1 times d, which is 2...