00:01
So we have a riverbank, and then we have 3 ,000 yards of fence.
00:09
And so that are going to be forming a rectangular plot.
00:15
And so if i label this x and this x and this y, we know that 2x plus y would have to equal 3 ,000 yards, or the y value would have to end up being 3 ,000 minus 2x.
00:32
And we want to optimize the area.
00:36
So we want a function in just one variable x, and we know that the product of these two, and this is 3 ,000 minus 2x, we know that the product of the length times the width, the x times the 3 ,000 minus 2x.
00:53
That will give us our area, and why don't we distribute? so we have 3 ,000x minus 2x squared.
01:00
So we have a nice quadratic function.
01:02
And we could actually figure the answer out to this without using any calculus because we know that this quadratic has a zero here and it has a zero at, if i divide that, that'd be at 1 ,500.
01:16
And we know it opens downward.
01:18
So like i said, we could figure out that this area function has a max up here.
01:23
But using calculus, we would say, well, hey, let's find the first derivative.
01:27
And we want to find where the slope is zero, which again, we can see from the picture, it's going to end up being at 7.
01:33
750 yards...