Quiz 5 solutions are up on the Web Page. As for program 7, the book
suggests using tincr rather than xincr. This is due to the fact that
parametric functions are not always functions in terms of x and y.
For example, x = cos(t), y = sin(t) generates a unit circle around the
origin. A circle is not a function in terms of x and y (x=0 gives two
values of y, -1 and 1), but it is a function of t from 0 to 2pi (each
(x,y) pair of our circle corresponds to exactly one t on 0 to 2pi). For
this reason you can't really work with xincr (you have no idea how
many y values you'll need to test for), but you can work with tincr.
However, when you hit a golf ball, its trajectory is a parabola, which
we know is a function in (x,y) coordinates. Our equations were
x = vtcos(theta) and y = vtsin(theta) - 32t^2, so we can write y in terms of x
by solving the x equation for t and then plugging that into the y equation.
So we get an equation y = f(x), and we can use xincr normally, even though
this is a parametric equation.