@gkokovidis 

I'll explain myself better: My homework is to plot the graph of f in it's recursive form and then compare between it and the graph of f in it's direct form (this is the plot that you gave). My goal is to get something like that: i.imgur.com/uzfGsYh.png. Thanks for your help! 

@Axel Vogt 

thanks for your help, but how from this I can plot the graph of the function? I'm trying to do that

but I keep getting errors.