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First. <u>Finding the x-intercepts of </u>
![W(x)](https://tex.z-dn.net/?f=W%28x%29)
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Let
![W(x)](https://tex.z-dn.net/?f=W%28x%29)
be the change in water level. So to find the
x-intercepts of this function we can use
The Rational Zero Test that states:
To find the zeros of the polynomial:
We use the
Trial-and-Error Method which states that a factor of the constant term:
![a_{0}](https://tex.z-dn.net/?f=a_%7B0%7D)
can be a zero of a polynomial (the x-intercepts).
So let's use an example:
Suppose you have the following polynomial:
where the constant term is
![a_{0}=6](https://tex.z-dn.net/?f=a_%7B0%7D%3D6)
. The possible zeros are the factors of this term, that is:
![1, -1, 2, -2, 3, -3, 6 \ and \ -6](https://tex.z-dn.net/?f=1%2C%20-1%2C%202%2C%20-2%2C%203%2C%20-3%2C%206%20%5C%20and%20%5C%20-6)
.
Thus:
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![W(1)=0 \\ W(-1)=0 \\ W(2)=-12 \\ W(-2)=0 \\ W(3)=0 \\ W(-3)=48 \\ W(6)=840 \\ W(-6)=1260](https://tex.z-dn.net/?f=W%281%29%3D0%20%5C%5C%20W%28-1%29%3D0%20%5C%5C%20W%282%29%3D-12%20%5C%5C%20W%28-2%29%3D0%20%5C%5C%20W%283%29%3D0%20%5C%5C%20W%28-3%29%3D48%20%5C%5C%20W%286%29%3D840%20%5C%5C%20W%28-6%29%3D1260)
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From the foregoing, we can affirm that
![1, -1, -2 \ and \ 3](https://tex.z-dn.net/?f=1%2C%20-1%2C%20-2%20%5C%20and%20%5C%203)
are zeros of the polynomial.
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Second. <u>Construction a rough graph of</u>
![W(x)](https://tex.z-dn.net/?f=W%28x%29)
Given that this is a polynomial, then the function is continuous. To graph it we set the roots on the coordinate system. We take the interval:
![[-2,-1]](https://tex.z-dn.net/?f=%5B-2%2C-1%5D)
and compute
![W(c)](https://tex.z-dn.net/?f=W%28c%29)
where
![c](https://tex.z-dn.net/?f=c)
is a real number between -2 and -1. If
![W(c)>0](https://tex.z-dn.net/?f=W%28c%29%3E0)
, the curve start rising, if not, the curve start falling. For instance:
![If \ c=-\frac{3}{2} \\ \\ then \ w(-\frac{3}{2})=-2.81](https://tex.z-dn.net/?f=If%20%5C%20c%3D-%5Cfrac%7B3%7D%7B2%7D%20%5C%5C%20%5C%5C%20then%20%5C%20w%28-%5Cfrac%7B3%7D%7B2%7D%29%3D-2.81)
Therefore the curve start falling and it goes up and down until
![x=3](https://tex.z-dn.net/?f=x%3D3)
and from this point it rises without a bound as shown in the figure below