The student does NOT have to implement the differentiator. The
lab might read as if implementing the differenetiator is part of
the task. The goodie provides it.
The formula must have only one variable: x.
The formula must have only binary expressions.
How is the find-zero supposed to find a zero when the value of the
fn is the same sign at both ends? Does it pursue bisection until
the interval is length eps? This is beyond any lab code....
Student must get graphing code from
plot
in graph-it.scm goodie.
They can call the plot routine, after loading the draw and graph-it goodies.
The find-zero code is a simple extension of the cube-root code
in Chapter 2.