00:01
Okay, for number 25, we have some information here.
00:05
We have an r of x and a c of x.
00:08
They give these two equations to us and the represent the total cost and the total revenue.
00:12
The profit is defined in the book as being the revenue minus the cost, which makes sense.
00:17
That's how you get profit.
00:19
And we need to find the maximum profit and the number of units sold to get that, to achieve that.
00:25
So most of our calculations are going to be based on the profit equation.
00:32
So let's go ahead and write that out in full.
00:34
This profit p of x, let's go ahead and put our pieces together here.
00:40
It's equal to 2x, which we get from above, minus this delightfully easy to write a bunch of numbers.
00:57
There we go.
00:58
Actually, this is pretty realistic.
01:00
I mean, there wouldn't just be integers in real life.
01:03
Go ahead and i'm going to make sure this is simplified as much as i can.
01:09
So this negative, this minus, it has to be carried out through each term.
01:15
Otherwise, you will not get the right answer.
01:23
Okay? things are going good so far.
01:26
We can bring our xs together and say 1 .4x minus 0 .01x squared.
01:38
Very small.
01:40
Minus 30.
01:42
Okay.
01:43
Now, what we need to do is we need to take the derivative of this and then set it to 0.
01:49
What this does is it allows us when we're visualizing the profit curve, there's this mystery spot here.
01:55
There's this x value.
01:57
And at that x value, there is a slope of 0...