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# Applying functions

Let's make a function to determine phases or the start and end of our graph's cycles. We'll write a function that finds the `x` intercepts of both the polynomial and sine graphs. Recall that these two functions appear as follows:

```(defn polynomial [a b c x]
(->
(+ (* a
(Math/pow x 3))

(* b
(Math/pow x 2)))
(- (* c x))))

(defn sine [a b d x]
(- (* a
(Math/sin (* b
(- x
(/ Math/PI 2)))))
d))```

Looking again at the representative graphs, the first thing to note is a constant x intercept of x=0. Next, if we go in either direction, the graph goes in a particular direction, then returns to pass through x, and winds back up again:

The graph ...

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