00:01
So, in the question we are given sn ,1 equals to 1 plus 2 plus 3 plus up to plus n into n plus 1 divided by 2.
00:11
So now, we will check this for n greater than or equal to 1.
00:17
So that is first term when n equals to 1.
00:22
So lhs will be equal to 1 and rhs will be equal to 1 into 1 plus 1 divided by 2.
00:29
So this will be equal to 1.
00:30
So therefore, we get that lhs equals to rhs.
00:35
So now for n equals to 2.
00:37
So the sum of first two terms.
00:44
So we will get that lhs equals to 1 plus 2 equals to 3 and rhs will be equals to 2 into 2 plus 1 divided by 2.
00:55
So this is equals to 3.
00:57
Now for n equals to 3, the lhs will be equals to 1 plus 2 plus 3 which is equals to 6 and rhs will be equals to 3 into 3 plus 1 divided by 2 and this is also equals to 6.
01:11
So now for n equals to 4.
01:16
So we will get that lhs is equals to 1 plus 2 plus 3 plus 4.
01:23
This is equals to 10 and rhs is equals to 4 into 4 plus 1 divided by 2 and this is also equals to 10.
01:31
So therefore, we get that for s, n comma 2 which is given 1 square plus 2 square plus 3 square plus up to n into n plus 1 into 2n plus 1 divided by 6.
01:45
So we need to prove this...