00:01
Okay, so let's firstly just quickly recall what it means for the limit of the function f of x at x equals c to be l.
00:16
That means that for all epsilon greater than zero, there exists a delta which can depend on epsilon greater than zero, such that if x is within delta of c, then f is within epsilon of l.
00:37
So in this case, we've got that our function f is equal to 3x plus 2.
00:44
We're looking at the limit as x tends to c equals zero, and our limit l is 2.
00:52
And we're picking epsilon to be 0 .5.
00:56
And we want to find a delta such that we can show this is satisfied.
01:03
And indeed, several of these deltas would suffice.
01:07
So for example, i'll pick delta equals 0 .027, recurring, because if you draw a graph of 3x plus 2, for x going from minus 0 .027 recurring to plus 0 .027 recurring, then you find that you get something like this, it's obviously a linear graph, centred about 2.
01:40
And the max it goes up to is just above 2 .05.
01:48
And the min is just below 1 .95.
01:52
And so we can clearly see that all of this is within the range.
01:58
So fx minus the limit 2 is within about 0 .07, which is indeed less than 0 .5, which is the epsilon that we're after.
02:15
Part b says demonstrate why the delta that you did not check does not suffice...