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Question
Math
Posted 8 months ago

- Draw the phase portrait for the logistic equation
dydx=y(aby)a,b>0.
\frac{d y}{d x}=y(a-b y) \quad a, b>0 .

and find the limit of the population y(x)y(x) as the time xx goes to infinity.
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Answer from Sia
Posted 8 months ago
Solution by Steps
step 1
The given logistic equation is dydx=y(aby)\frac{d y}{d x} = y(a - b y) where a,b>0a, b > 0
step 2
To draw the phase portrait, we need to identify the equilibrium points by setting dydx=0\frac{d y}{d x} = 0
step 3
Solving y(aby)=0y(a - b y) = 0 gives the equilibrium points y=0y = 0 and y=aby = \frac{a}{b}
step 4
The phase portrait can be drawn by plotting these equilibrium points on the yy-axis and analyzing the behavior of yy around these points
step 5
For y<0y < 0, dydx>0\frac{d y}{d x} > 0 and yy increases. For 0<y<ab0 < y < \frac{a}{b}, dydx>0\frac{d y}{d x} > 0 and yy increases. For y>aby > \frac{a}{b}, dydx<0\frac{d y}{d x} < 0 and yy decreases
step 6
The limit of the population y(x)y(x) as xx goes to infinity can be found by considering the equilibrium points
step 7
As xx \to \infty, y(x)y(x) approaches the stable equilibrium point, which is y=aby = \frac{a}{b}
Answer
The phase portrait shows that y=0y = 0 is an unstable equilibrium and y=aby = \frac{a}{b} is a stable equilibrium. The limit of the population y(x)y(x) as xx goes to infinity is ab\frac{a}{b}.
Key Concept
Logistic Equation Equilibrium Points
Explanation
The logistic equation dydx=y(aby)\frac{d y}{d x} = y(a - b y) has equilibrium points at y=0y = 0 and y=aby = \frac{a}{b}. The population y(x)y(x) will approach the stable equilibrium point ab\frac{a}{b} as time xx goes to infinity.

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