00:01
So in this question, we're considering the function f of x, y, equals the natural log of x squared plus y squared.
00:09
And the first thing we're concerned with is the continuity of this function, yes? and so what do i know about a domain of a natural log function? so if i'm considering the continuity, we will be continuous whenever x squared plus y squared is greater than zero, right? i can only take the natural log of something that is positive.
00:37
So in order to be in the domain of the ln of x squared plus y squared, whatever i'm taking the ln of, in this case, x squared plus y squared, must be greater than zero.
00:49
However, notice that x squared is always non -negative, and y squared is also non -negative, right? so the only time that we would have a discontinuity on this is if x and y were both zero, right? because if x and y were both zero, i'd be taking the ln of zero, which is it possible? however, as long as x and y are both non -zero, then my x squared plus y squared, as long as at least one of them is non -zero, then that's that sum will be positive.
01:33
So the only time we have a discontinuity is when our xy is 0 .0.
01:42
And so we would say that we are continuous over all of r2, over all of r2 except when i am at the origin...