do some demos on the convergence of like...the bisection method vs secant method vs newton's method
if you're skilled, derive the convergence rates for those 3...this is kind of hard, so if you dont' get it, just make some graphs
edit: or talk about when the above mentioned methods can be made to fail/converge very poorly
edit2: or look up something called the "Romberg Method" and demonstrate how it can be used to speed up the trapezoid rule (integration), & when/why romberg will fail.
edit3: show why you CANNOT simply continue to decrease h when you do numerical derivatives to increase accuracy