00:01
We're being asked to find the sum of this series.
00:03
Well, let's pick out the information we know.
00:05
When we know the first term is 5, so a sub 1 is equal to 5, and we know the last term is 49, so we know that a sub n is equal to 49.
00:15
Now, this is an arithmetic series, because to get from one term to the next, we simply keep adding 4.
00:21
So, d is equal to 4.
00:23
So we just need to find n.
00:25
To do this, we're going to use the formula to find the nth term in an arithmetic sequence, which is a sub n equals a sub 1 plus the quantity of m minus 1 times d.
00:36
So let's substitute in the values that we know.
00:39
Well, we're going to have 49 equals 5 plus the quantity of n minus 1 times 4.
00:46
So let's solve for n.
00:48
So i'm going to subtract 5 from both sides...