00:01
Okay, in this problem, we're asked to find the eighth term of an arithmetic sequence.
00:05
So we're looking for a8, and we're told that the fourth term is 19, and the 15th term is 52.
00:22
Okay.
00:23
So what are the two things? what are some of the things we need for an arithmetic sequence? we need the common difference, and we need the first term.
00:31
So we don't have any of those.
00:32
If we can get those, we're kind of basically done.
00:36
Now, finding the common difference can be tricky when you have non -consecutive terms, but we've got a little formula for this.
00:43
Okay, so we can find the common difference here by doing a -15 minus a -4, subtracting our non -consecutive terms, and then dividing this by how far apart they are.
00:56
So essentially dividing this by 15 minus 4.
01:00
Okay? so in our problem, we'll have 52 minus 19, divided by 15 minus 4.
01:08
52 minus 19 should be 33.
01:16
15 minus 4 should give us 11...