00:01
Hello, numerate, welcome back.
00:02
Okay, we're in chapter 4, section 4 of thomas's calculus 14th edition, page 213, number 107.
00:16
And they're talking about marginal clause.
00:18
So they give a function.
00:24
It looks like on a closed interval from, whoops, closed interval, from 20, x equals 20, these are x values, to x equals 120.
00:46
And we're given c is a function of x.
00:48
So c is the cost of producing x widgets.
00:52
And to talk about marginal cost, the marginal cost has to do the rate of change.
00:55
Let's say that's c prime, although in economics class i actually define it differently.
00:59
But let's say that's c prime.
01:01
C prime has no sign change here.
01:03
It's always positive.
01:04
It's always increasing.
01:05
Okay.
01:06
The question is, approximately what production level does the marginal cost change from decreasing to increase it? so i think we're talking about the second derivative...