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After a certain drug is injected into a patient, the concentration \(c\) of the drug in the bloodstream is monitored. At time \(t \geq 0\) (in minutes since the injection), the concentration (in \(\mathrm{mg} / \mathrm{L}\) ) is given by $$ c(t)=\frac{30 t}{t^{2}+2} $$ (a) Draw a graph of the drug concentration. (b) What eventually happens to the concentration of drug in the bloodstream?

Short Answer

Expert verified
The concentration peaks and then approaches zero as time goes on.

Step by step solution

01

Understand the Function

The function given is \(c(t)=\frac{30t}{t^{2}+2}\), which represents the drug concentration over time. It is a rational function where the numerator is linear and the denominator is quadratic.
02

Identify Key Features of the Graph

To graph \(c(t)\), find the intercepts, asymptotes, and behavior as \(t\) approaches infinity. The y-intercept can be found by plugging \(t = 0\), giving \(c(0) = 0\). There are no x-intercepts since the numerator is zero only when \(t = 0\). There are no vertical asymptotes, as the denominator \(t^2 + 2\) is never zero.
03

Calculate the Limit as t Approaches Infinity

Evaluate \(\lim_{{t \to \infty}} \frac{30t}{t^{2}+2} \) using L'Hôpital's rule. Differentiating the numerator and the denominator gives \(\lim_{{t \to \infty}} \frac{30}{2t} = 0\). This suggests a horizontal asymptote at \(y = 0\).
04

Sketch the Graph

Based on the intercepts and asymptotic behavior, sketch the graph of \(c(t)\). Start at the origin, increase to a maximum point, and then gradually decrease, approaching \(y = 0\) as \(t\) increases.
05

Interpret the Long-term Behavior

The graph shows that after reaching a peak, the concentration decreases towards zero. As time continues, the concentration in the bloodstream eventually approaches zero.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Asymptotic Behavior
When exploring the asymptotic behavior of rational functions like \(c(t)=\frac{30 t}{t^{2}+2}\), we seek to understand how the function behaves as \(t\) becomes extremely large or extremely small. Asymptotic behavior for this function is primarily determined by horizontal asymptotes, since there are no vertical asymptotes in this scenario.

A horizontal asymptote occurs when the outputs of a function approach a constant value as \(t\) approaches infinity. For \(c(t)\), as \(t\) increases, the quantity \(t^2\) in the denominator grows much faster than \(30t\) in the numerator. This growth causes the entire expression to approach zero, as calculated using L'Hôpital's Rule.

Understanding this behavior is crucial in real-world contexts, such as drug concentration in blood, where we deduce that over time, the drug's effectiveness diminishes and approaches a baseline level, which is zero in this case. Knowing this can be vital for determining dosing schedules in medical treatments.
Graphing Functions
Graphing functions, especially rational functions like \(c(t)=\frac{30 t}{t^{2}+2}\), allows us to visually interpret and analyze the behavior of real-world scenarios such as drug concentration over time. To graph this function, several key features must be identified: intercepts, asymptotes, and general behavior over its domain.

  • Intercepts: For \(c(t)\), the y-intercept can be found by setting \(t=0\). This calculation provides \(c(0) = 0\). There are no x-intercepts as the function never crosses the x-axis meaning there's no solution where the function equals zero unless \(t=0\).
  • Asymptotes: Understanding there are no vertical asymptotes because \(t^2+2\) never becomes zero highlights how the function's domain is unrestricted for all real numbers. The horizontal asymptote at \(y=0\) impacts the function's long-term behavior.
To graph, we plot from the origin, observe the rise to a peak, then a gradual decline approaching the horizontal asymptote. Such visual tools are critical in making predictions and understanding trends in data like concentration changes.
Limit Calculation
Calculating limits helps us understand the behavior of a function as the variable approaches a particular value (like infinity). For \(c(t)=\frac{30 t}{t^{2}+2}\), the limit calculation as \(t\to \infty\) is essential to predicting the concentration's eventual value. This is achieved using L'Hôpital's Rule, a calculative technique for limits of indeterminate forms.

By differentiating the numerator and denominator separately, we find:\[\lim_{{t \to \infty}} \frac{30}{2t} = 0\]This result indicates that the concentration decreases to zero over time.

Calculating limits in this context clarifies the final outcome of processes, like drug concentration, in complex systems. It reflects why certain dosages cannot sustain long-term effectiveness and why repeated doses might be necessary to maintain therapeutic concentration levels. This understanding is foundational in fields involving dynamic concentration changes such as pharmacokinetics and other applied sciences.

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Most popular questions from this chapter

Find the intercepts and asymptotes, and then sketch a graph of the rational function and state the domain and range. Use a graphing device to confirm your answer. $$r(x)=\frac{2 x^{2}+2 x-4}{x^{2}+x}$$

The quadratic formula can be used to solve any quadratic (or second-degree) equation. You might have wondered whether similar formulas exist for cubic (thirddegree), quartic (fourth-degree), and higher-degree equations. For the depressed cubic \(x^{3}+p x+q=0,\) Cardano (page 274) found the following formula for one solution: $$x=\sqrt[3]{\frac{-q}{2}+\sqrt{\frac{q^{2}}{4}+\frac{p^{3}}{27}}}+\sqrt[3]{\frac{-q}{2}-\sqrt{\frac{q^{2}}{4}+\frac{p^{3}}{27}}}$$ A formula for quartic equations was discovered by the Italian mathematician Ferrari in \(1540 .\) In 1824 the Norwegian mathematician Niels Henrik Abel proved that it is impossible to write a quintic formula, that is, a formula for fifth-degree equations. Finally, Galois (page 254) gave a criterion for determining which equations can be solved by a formula involving radicals. Use the cubic formula to find a solution for the following equations. Then solve the equations using the methods you learned in this section. Which method is easier? (a) \(x^{3}-3 x+2=0\) (b) \(x^{3}-27 x-54=0\) (c) \(x^{3}+3 x+4=0\)

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Graph the rational function, and find all vertical asymptotes, \(x\) - and \(y\) -intercepts, and local extrema, comect to the nearest decimal. Then use long division to find a polynomial that has the same end behavior as the rational function, and graph both functions in a sufficiently large viewing rectangle to verify that the end behaviors of the polynomial and the rational function are the same. $$r(x)=\frac{4+x^{2}-x^{4}}{x^{2}-1}$$

Recall that the symbol \(\bar{z}\) represents the complex conjugate of \(z .\) If \(z=a+b i\) and \(w=c+d i,\) prove each statement. $$\overline{\bar{z}}=z$$

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