00:01
In this problem, we have been asked to show that n choose k is equal to n choose n minus k.
00:10
So for that purpose, recall the formula for n choose r, that is n factorial over r factorial times n minus r factorial.
00:20
So let us consider the left hand side.
00:23
Here we have n choose k.
00:25
So that will be n factorial over k factorial times n minus k factorial.
00:34
So let's rewrite this.
00:36
Instead of k, let us write that as n minus n minus k.
00:42
We can write k as n minus of n minus k.
00:45
And here we have n minus k factorial.
00:49
And let's just rearrange the terms in the denominator factors.
00:53
So n minus k factorial times n minus n minus...