In Exercise, use the viewing windows found in Exercise 1–3.(a) When was the concentration...

In Exercise, use the viewing windows found in Exercise 1–3.

(a) When was the concentration of the medication in Exercise 1 at its peak?

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(b) Use the trace feature to determine approximately when the concentration dropped below 10 milligrams per liter and stayed below that level.

Exercises 1–3

In each of the applied situations in Exercise, find an appropriate viewing window for the equation (that is, a window that includes all the points relevant to the problem but does not include large regions that are not relevant to the problem, and has easily readable tick marks on the axes). Explain why you chose this window. [Hint: You can’t make a negative number of shirts.]

1. Beginning in 1905 the deer population in a region of Arizona rapidly increased because of a lack of natural predators. Eventually food resources were depleted to such a degree that the deer population completely died out. In the equation y = −.125x5 + 3.125x4 + 4000, y is the number of deer in year x, where x = 0 corresponds to 1905.

2. A cardiac test measures the concentration y of a dye x seconds after a known amount is injected into a vein near the heart. In a normal heart

 y = −.006x4 + .14x3 − .053x2 + 179x.

3. The concentration of a certain medication in the bloodstream at time x hours is approximated by the equation

where y is measured in milligrams per liter. After two days the medication has no effect.