$解：(2)把x=k代入y=-x-1，得y=-k-1，$
$则A_1的坐标是(k，-k-1)；$
$把x=k代入y=\frac {1}{x}得：y=\frac {1}{k}，$
$则B_1的坐标是(k，\frac {1}{k})；$
$把y=\frac {1}{k}代入y=-x-1得：\frac {1}{k}=-x-1$
$解得：x=-\frac {k+1}{k}，即A_2的坐标是(-\frac {k+1}{k}，\frac {1}{k})；$
$把x=-\frac {k+1}{k}代入y=\frac {1}{x}得：y=-\frac {k}{k+1}$
$则B_2的坐标是(-\frac {k+1}{k}，-\frac {k}{k+1})$
$把y=-\frac {k}{k+1}代入y=-x-1，得：x=-\frac {1}{k+1}$
$即A_3的坐标是(-\frac {1}{k+1}，-\frac {k}{k+1})；$
$把x=-\frac {1}{k+1}代入y=\frac {1}{x}得：y=-k-1$
$则B_3的坐标是(-\frac {1}{k+1}，-k-1)$
$把y=k+1代入y=-x-1得x=k，则A_4的坐标是(k，-k-1)，即A_1$
$则点A_{n}的横坐标分别是：k，-\frac {k+1}{k}，-\frac {1}{k+1}，···三个循环一次$
