PHP - First and last day of last month.

Hi, I need to know the first and the last day of the current month and last month.

I use this:

   function firstOfMonth()
                        {
                            return date("Y-m-d H:i:s", strtotime(date('m') . '/01/' . date('Y') . ' 00:00:00'));
                        }
                        function lastOfMonth()
                        {
                            return date("Y-m-d H:i:s", strtotime('-1 second', strtotime('+1 month', strtotime(date('m') . '/01/' . date('Y') . ' 00:00:00'))));
                        }

to find out the first and the last date of the current month, but how do I find out the first and the last day of the last month?

Thank you.