FECHAS - RECUPERAR 1ER Y ÚLTIMO DIA DE LA SEMANA / MES (Ej. MonthCalendar)

'1er día de la semana 
MonthCalendar.SelectionStart.Date.AddDays(1 - (MonthCalendar.SelectionStart.Date.DayOfWeek))
'Último día de la semana
MonthCalendar.SelectionStart.Date.AddDays(7 - (MonthCalendar.SelectionStart.Date.DayOfWeek))


'1er día del mes
Format(MonthCalendar.SelectionStart.Date.AddDays,"01/MM/yyyy")
'Último día del mes
MonthCalendar.SelectionStart.AddDays(Date.Today.DaysInMonth(Date.Today.Year, Date.Today.Month) - Date.Today.Day)