This is a three-part question:
a. the graph y = f(x) in the xy-plane has parametrization x=x, y=f(x), and vector formula r(x) = xi + f(x)j. Use this to show that if f is twice-differentiable, then
b. use the formula for k in part a to find the curvature of y = ln(cosx) when -pi/2 < x < pi/2.
c. show that the curvature is zero at the point of inflection.