00:01
Hi, if you look at an arithmetic sequence that is given as a, a plus g, a plus 2d, and so on, we have a plus n minus 1d.
00:13
Right, so we have the n -s term is given as a -n that equals a plus n minus 1 times g, right? where you have a is the first term, and we have the number of terms, and then we have d, the common difference, right? the common difference.
00:40
So we're given here we're given here a 11 is 65 right a 11 that is 65 next we're given a 25 is 149, 149 this is given to us we're given here a 11 as 65 a 25 25 25 is 149 right and to find out a 400 so so a 400 is going to find out.
01:16
The method is apply the n -fm formula.
01:18
So that is coming out to be well given as a is the first term.
01:22
So a plus 11 minus 1 times d.
01:25
These are common difference.
01:27
That equals 65.
01:28
All right.
01:29
So a plus 10d that equals 65.
01:33
If you get here.
01:33
And we just solve this.
01:35
We get a plus 25 minus 1 into d.
01:39
That equals 1 .49.
01:42
Right.
01:42
So we get a plus 24 d that equals 149.
01:47
We have two equations here...