Suppose that the concentration of medication in the bloodstream follows M? +4 3- М Mt+1 M - %3D where M is the medication in the bloodstream given in mg/L. (Here the 4 is the supplement and the fraction term deals with the absorption rate of the mediation.) (a) Find all biological equilibria of this system.

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**Problem 10: Medication Concentration in the Bloodstream**

Suppose that the concentration of medication in the bloodstream follows the formula:

\[ M_{t+1} = M_t - \frac{M_t^2}{3 - M_t} + 4 \]

where \( M_t \) is the medication in the bloodstream given in mg/L. (Here the 4 is the supplement and the fraction term deals with the absorption rate of the medication.)

**(a) Find all biological equilibria of this system.**

**Solution:**

Let \( x \) be the equilibrium concentration.

\[ x = x - \frac{x^2}{3-x} + 4 \]

\[ x^2 = \frac{x^2}{3-x} \cdot (3-x) \]

\[ x^2 = 4(3 - x) \]  
\[ x^2 = 12 - 4x \]  
\[ x^2 + 4x - 12 = 0 \]

**Solving the quadratic equation:**

\[ (x + 6)(x - 2) = 0 \]

The solutions are:

\[ x = -6 \quad \text{and} \quad x = 2 \]

Reject \( x = -6 \) because concentration cannot be negative.

Thus, the biological equilibrium is \( x = 2 \).

**(b) For each biological equilibrium, decide if it is stable and also if it oscillates.**

**Analysis:**

Calculate the derivative \( f'(X) \):

\[ f'(X) = 1 - \frac{(3-X)(2X) - X^2 (1)}{(3-X)^2} \]

\[ f'(2) = 1 - \frac{(3-2)(2 \cdot 2) - (2)^2}{(3-2)^2} \]

\[ = \left| 1 - \frac{(1)(4) - 4}{1^2} \right| \]

\[ = |1 - 0| = |1| = 1 \]

The magnitude is 1, indicating a neutral stability with no oscillation at the equilibrium \( x = 2 \).
Transcribed Image Text:**Problem 10: Medication Concentration in the Bloodstream** Suppose that the concentration of medication in the bloodstream follows the formula: \[ M_{t+1} = M_t - \frac{M_t^2}{3 - M_t} + 4 \] where \( M_t \) is the medication in the bloodstream given in mg/L. (Here the 4 is the supplement and the fraction term deals with the absorption rate of the medication.) **(a) Find all biological equilibria of this system.** **Solution:** Let \( x \) be the equilibrium concentration. \[ x = x - \frac{x^2}{3-x} + 4 \] \[ x^2 = \frac{x^2}{3-x} \cdot (3-x) \] \[ x^2 = 4(3 - x) \] \[ x^2 = 12 - 4x \] \[ x^2 + 4x - 12 = 0 \] **Solving the quadratic equation:** \[ (x + 6)(x - 2) = 0 \] The solutions are: \[ x = -6 \quad \text{and} \quad x = 2 \] Reject \( x = -6 \) because concentration cannot be negative. Thus, the biological equilibrium is \( x = 2 \). **(b) For each biological equilibrium, decide if it is stable and also if it oscillates.** **Analysis:** Calculate the derivative \( f'(X) \): \[ f'(X) = 1 - \frac{(3-X)(2X) - X^2 (1)}{(3-X)^2} \] \[ f'(2) = 1 - \frac{(3-2)(2 \cdot 2) - (2)^2}{(3-2)^2} \] \[ = \left| 1 - \frac{(1)(4) - 4}{1^2} \right| \] \[ = |1 - 0| = |1| = 1 \] The magnitude is 1, indicating a neutral stability with no oscillation at the equilibrium \( x = 2 \).
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