Points of Inflection
The value f '(x) is the gradient at any point but often we want to find the Turning or Stationary Point (Maximum and Minimum points) or Point of Inflection
These happen where the gradient is zero, f '(x) = 0.
Critical Points include Turning points and Points where f ' (x) does not exist.
f ''(x) is negative the function is maximum turning point
f ''(x) is zero the function may be a point of inflection
f ''(x) is positive the function is minimum turning point