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A playground is enclosed and subdivided by 1700 feet of
fencing, as shown in the figure to the right.
Use a graphing utility to graph A of X equal X divided by or X *
1700 -, 2 X all divided by three, which expresses the area
of the playground A in terms of one of its dimensions X.
I'm actually going to show that how to do this without a
calculator.
So the first thing is to realize that two X + 3 Y equals the
1700.
So I'm going to solve for Y, subtract my 2X divided by three
and I see that y = 1700 - 2 X divided by three.
So to find the area, the area is just going to be X * y or X *
1700 -, 2 X over three.
If I distribute this out, I realize that this is just a
graph of a parabola that's going to be going opening downwards,
hence it'll have a maximum point.
If I look at the X intercepts, the X intercepts come from
setting the numerator equal to 0.
So if you thought about setting the numerator equal to 0, we
have the X times the 1700 -, 2 X all divided by three.
Well if we just set the numerator equal to 0, we can see
that X = 0 and X = 1700 / 2 which is 8:50.
So the X intercepts are 00 and 8:50 zero.
The vertex has to be exactly in the middle because of symmetry.
So if I thought about taking the 2X intercepts and adding them
together and dividing by two, that would be my axis of
symmetry.
So from the axis of symmetry, once I get this X value, I can
just stick it into the function.
Actually, I guess this should have said A because we're using
A's, but we can stick it into the function to find the Y.
So my X value or my vertex is 425 and my area or my output is
361,250 all over three.
So if we know that X is 425, we can find our Y simply by
substituting 1700 - 2 * 425 all over three.
That's about 283 rounding.
And then to find the area we can just go X * 17 - 2 X over three.
It should also be the Y value of our vertex and it is so 120,417
feet squared for the area.