00:01
We're being asked to find the sum of this particular arithmetic sequence.
00:05
Well, what do we know about this sequence? well, we know the first term, a sub 1, is equal to 1.
00:10
Now, this last term is in terms of n, which tells us that a sub n is equal to 2n minus 1.
00:18
So, what we're going to do is we're going to use our general formula, s subn, is equal to n divided by 2, times the quantity of a sub 1 plus a sub n.
00:27
Now, as you can see, we don't know how many specific terms are in the sequence, we're just calling it n.
00:33
So we're going to substitute a sub 1 and a subn into our formula...