00:01
So in this problem, we are given the set a equals all y in the metric space x, such that the distance from x to y is greater than r.
00:13
So we are given a metric space x and a distance d on the metric space x.
00:18
And a is the set of all y is in x such that the distance of y from x is greater than r.
00:24
And we're going to show that this set a is open in x.
00:29
So first we are going to take any y in a, then the distance from x to y is, let's say r1, then r1 would be greater than r by the definition of a.
00:45
Now next, choose any r2 that is less than r1 minus r.
00:51
So r1 is greater than r so r1 minus r is a positive quantity.
00:55
And we're going to choose any r2 that is less than r1 minus r.
00:59
And then we're going to consider the ball of radius r2 around the point y.
01:06
And if we can show that this ball is inside a, then we have proven that a is open.
01:13
So next denote by b the open ball of radius r2 about the point y...