You can use GeoGebra to find the stationary points of a function. One method involves using CAS. Another way is to use Algebra View and Graphics View.                                                                                                                                                                                                                                          
     Recall that Solve  yields exact answers (fractions and roots), while 
Solve Numerically  yields approximated answers given as decimal numbers. 
     GeoGebra Instruction 1
CAS CAS     under         View     in         Menu.         f(x):=.         Then         press         Enter.         Derivative =0     after         the         expression         and         press         Solve Solve     Numerically f(x-value)     and         then         press         Enter.         Do         this         for         all         the         -values         you         have         found.         Graphics     View.         
      
     If you only want to find the extrema (maxima or minima) of a function, you can just use Graphics View. 
     GeoGebra Instruction 2
Graphics View Algebra     View     and         Graphics     View     under         View     in         Menu.         Algebra     View     and         then         press         Enter.         Extremum(<Function>, <Start x-Value>, <End x-Value>)
in Algebra View.         
Enter the function name (,         ,         and so on) for <Function>. For <Start> and <End>, choose a         sufficient interval based on the plotted graph. For <Start>, choose an         -value         to the left of all the extrema of the graph, and for <End>, choose an         -value         to the right of all the extrema of the graph.