00:01
Let's use induction in part a to show that this sequence is increasing.
00:06
So first, let's just state what we're approving.
00:13
So it's increasing.
00:17
So we do proof by induction.
00:29
So now we have our base case.
00:33
This is where we'd like to show that a1 is less than or equal to a2.
00:40
So we have a2 equals radical 2 plus a1 using the formula so that's just radical 2 plus root 2 and this is definitely bigger than root 2 because here we're adding something so in other words this thing right here is bigger than root 2 if x is bigger than 0 because we know this the square root graph is increasing so the larger the input the larger the square root.
01:19
So this checks the base case for us.
01:23
Now we do the inductive step.
01:25
Second part of the induction.
01:30
So we'd like to go ahead and suppose a .n minus 1 is less than or equal to a .n.
01:41
Now we want to show that this inequality is true after you increase the n by one on both sides there.
01:57
So let's go ahead and write this on the next page.
02:05
This was given.
02:09
Recall the formula for an.
02:16
So we would like to show, so here when we replace n with n plus one, recall the one that we wanted to show.
02:26
So keep this one in mind.
02:29
This is what we want.
02:33
Now this right hand side, we could expand this.
02:37
This is just radical 2 plus an.
02:41
So let me write this.
02:43
An plus 1 equals this just by using this formula up here.
02:49
This holds for all n.
02:53
So just using that there that justifies this.
02:56
Then this is bigger than or equal to radical 2 plus an minus 1.
03:02
And this is due to this fact over here that i'll have a arrow indicating.
03:10
And then this is equal to an...