Two young mathematicians discuss differential equations.
Check out this dialogue between two calculus students (based on a true
story):
-
Devyn
- Riley, check out this book, it has some cool applications of calculus:
The following differential equation can be used to model the
spread of an infectious disease:
\[ \mathrm {infect}'(t) = k\cdot \mathrm {infect}(t)\cdot (P-\mathrm {infect}(t)) \]
where \(k\) is a constant, \(\mathrm {infect}(t)\) is the
number of people infected by the disease on day \(t\), and \(P\) is the
size of the population vulnerable to the disease.
-
Riley
- Whoa. That’s like a formula for a derivative. Wow. Much calculus.
-
Devyn
- I wonder how you solve equations like this?
-
Riley
- I wonder if we can sometimes just use facts about the derivative to
give us an approximation for the function that models the spread of
infection?
Suppose your calculus class has had a freak outbreak of the
math-philia. Some
facts: We have around
\(200\) students in our class, we are now on the
\(23\)rd day of
the outbreak, and currently
\(100\) students are infected. Using the differential
equation
\[ \mathrm {infect}'(t) = k\cdot \mathrm {infect}(t)\cdot (P-\mathrm {infect}(t)) \]
we can model the spread of
math-philia by setting
\(k=0.001\). What is
\(\mathrm {infect}'(23)\)?
\[ \mathrm {infect}'(23) = \answer {10} \]
Do your best to explain why the equation
\[ \mathrm {infect}'(t) = k\cdot \mathrm {infect}(t)\cdot (P-\mathrm {infect}(t)) \]
is reasonable.
Don’t worry, just do
your best.