For example: I need to filter tasks for "Monday" and i don´t know how to do it.

I have tried in several ways but I can´t find the solution.

I done it for "Last Week" and "This Week":

<filter string="Last Week" name="last_week" separator="1" 
        domain="[('date', '&gt;=', ((context_today()+relativedelta(weeks=-2, days=1, weekday=0)).strftime('%Y-%m-%d'))), 
                ('date', '&lt;=', ((context_today()+relativedelta(weeks=-1,weekday=6)).strftime('%Y-%m-%d')))]"/> 

<filter string="This Week" name="this_week" separator="1" 
        domain="[('date', '&lt;=', ((context_today()+relativedelta(weeks=0, days=7, weekday=-1)).strftime('%Y-%m-%d'))), 
                ('date', '&gt;=', ((context_today()-relativedelta(weeks=1, weekday=0)).strftime('%Y-%m-%d')))]"/>