00:01
All right, so for the question that we're given today, we are asked, we need to show that if n and j are integers with j being greater than zero and greater than or less than, sorry, less than n, then we need to prove that n j is equal to n, n minus j.
00:28
And we need to conclude that pascal's triangle is symmetric with respect to the vertical lines drawn from the topmost entry.
00:37
So, for this question, we are going to start with n and j.
00:46
So that is equal to, using the formula that we know, by definition, it is n factorial over j factorial, n minus j factorial.
00:59
And we know that, sorry, i'm just going to write a little and right here, and we know that n minus j is equal to n factorial over n minus j factorial, and then n minus j factorial.
01:37
We know that these two things are true.
01:40
And this can actually be made a bit simpler by just turning it into this.
01:47
N factorial over n minus j factorial and j factorial.
01:58
And j factorial.
02:02
So now that we have that, we look at that with all the canceling of the jays and the ends on the bottom, but you're going to have with this.
02:08
And when we look up at the top, that appears to be the same...