A building that is 100 ft tall casts a shadow that makes a 30 degree angle with the ground. Approximately how long, in feet, is
2 answers:
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The ODE has an equilibrium point at
We want to be an unstable equilibrium solution - in other words, we want all solutions with initial condition
for
near 2 to diverge from
- so
.
Divergence from would require that for
, any solution is increasing, and for
, and solution is decreasing. In order for that to happen, we need
if , and
if .
Now we just pick to satisfy these conditions. An easy choice is
, which forces
, so that one possible ODE would be
I've attached a plot of the slope field to demonstrate the behavior of the solutions.
