00:01
In this question, we want to determine whether the submission of these to infinity, whether it converges or diverges.
00:09
So in part a, we want to find a simple formula for sn, the sum to n term.
00:17
So sn is actually k equals 1 to n, 1 over k plus 2, 1 over k plus 3.
00:28
Now, obviously, we need to split this into partial fraction.
00:32
So i'm going to let 1 over k plus 2 k plus 3 be equals to a over k plus 2 plus b over k plus 3 cross multiply we get this i'm going to let k equals to minus 2 on the left i have 1 on the right be a minus 2 plus 3 plus now minus 2 plus 2 be 0 so this part will go to 0 so i have 1 is equal to a.
01:14
Next, i'm going to let k equals to minus 3.
01:21
So i have from here, 1 equals to now, minus 3 plus 3 will be 0.
01:28
So this part goes to 0 plus b, minus 3 plus 2.
01:33
So i have 1 equals to minus b, so b equals to minus 1.
01:39
So here i can replace it with the partial fraction.
01:47
Of a is 1 over k plus 2 and b is minus 1.
01:53
So minus 1 over k plus 3.
01:56
Now obviously you can see from here we're using method difference.
02:00
Just sub in the first few values of k and the last few values of k.
02:04
So when k equals to 1, we have 1 3rd minus 1 quarter...