- #1
altegron
- 14
- 2
Homework Statement
Consider a population of individuals with a disease. Suppose that [tex]t[/tex] is the number of years since the onset of the disease. The death density function, [tex]f(t) = cte^{-kt}[/tex], approximates the fraction of the sick individuals who die in the time interval [t, t+Δt] as follows:
Fraction who die: [tex]f(t)\Delta t = cte^{-kt} \Delta t[/tex]
where [tex]c[/tex] and [tex]k[/tex] are positive constants whose values depend on the particular disease.
(a) Find the value of c in terms of k.
(b) Express the cumulative death distribution function in the form below. Your answer will be in terms of k.
[tex]
C(t)=\left\{\begin{array}{cc}A(t),& t < 0\\
B(t), & t \geq 0\end{array}\right
[/tex]
Homework Equations
[tex]P(t) = \int_{-\inf}^t p(x) dx[/tex]
The Attempt at a Solution
To solve part a, I know that [tex]\lim_{t\rightarrow\infty} P(t) = 1[/tex]. So c and k must have values so that it equals one. So I integrate [tex]f(t)[/tex] with the relevant equations to get:
[tex]
\frac{-(kt+1) \cdot e^{-kt} \cdot c}{k^2}
[/tex]
from negative infinity to t.
The problem is that this diverges to negative infinity and doesn't give me a meaningful answer. So what do I do?
Also, how do I get the the bar with a superscript and subscript for 'from a to b' in tex?