00:01
So we have an apartment complex whose profit is found by the p of x function, and we want to maximize profit.
00:06
So to maximize profit, we're going to find the derivative and then set that derivative equal to zero.
00:11
So p prime of x equals negative 20, x plus 1 ,700, set it equal to zero.
00:21
And i'm setting it equal to zero because if i were to consider the graph of this function, it's going to be an inverted parabolas, something like this.
00:28
And when we find the derivative, that's the slope of the tangent line.
00:31
At a specific point, and we want that derivative to be equal to zero because that is when our maximum would occur.
00:40
So when we have a flat line on top, we have a slope of zero.
00:43
That's when our maximum is going to occur.
00:45
So now i'm going to subtract 1 ,700 from both sides.
00:49
And when i divide by negative 20, i get x equals 85.
00:53
And so my profit is maximized when i have 85 of my apartment units rented out.
00:59
And if i go back and i plug in 85 for x, in my original profit function, i can figure out how much profit that would be.
01:06
So 85 squared is going to give me 7 ,225 times negative 10.
01:13
It's going to give me negative 72 ,250 plus 1 ,700 times 85 is going to give me 144 ,500.
01:25
And then we're going to subtract 41 ,000.
01:27
So when i do that arithmetic there, i get a total profit of $31 ,250.
01:37
So my profit is maximized at 85 units, and i get a total of $31 ,250.
01:46
The second question we're asked about is if we had some compact disks, and there's a couple of equations that they give us, they give us a price equation of negative 0 .000 ,000.
01:58
43x plus 8.
01:59
So p represents the price of each disc and d x represents the demand of those disks.
02:05
So our revenue can be found by taking the price of each disc, this right here, and multiplying it by the demand or however money we're going to sell.
02:13
So p times x.
02:14
So if i were to take my price function and multiply it times x, i'm going to get my revenue.
02:20
So it's going to give me negative 0 .0043x squared plus 8x...