How do you find the coordinates of stationary points on a graph?

First differentiate the function:  y = f(x)   =>   dy/dx = f'(x)

Then set dy/dx = 0 and find the solutions. i.e. solve 0 =  f'(x)

For each value of x that is a solution, substitute back into f(x) to get the y coordinates.

We now have the coordinates of the stationary points.