Find the coordinates and determine the nature of any stationary points on the graph of , where is the function defined by .
Start by finding
Solve to find the -coordinates of any stationary points
Substitute into to find the corresponding -coordinates
So the stationary points are and
Method 1: using the second derivative to test the points
Differentiate to find the second derivative
Now substitute in the -coordinates of the two stationary points
This will give the value of the second derivative at those points
That is less than zero, so is a local maximum point
That is greater than zero, so is a local minimum point
Method 2: using the first derivative to test the points
Test the values of at either side of the stationary points
(Note that, where applicable, is a very convenient test value!)
At the derivative changes from positive to negative, so that is a local maximum point
At the derivative changes from negative to positive, so that is a local minimum point
Note that for this function both stationary points are also turning points
is a local maximum point
is a local minimum point