$$\eqalign{
& y = {{mx - 1} \over {x + m}}\,\,\left( {x \ne - m} \right) \cr
& y' = {{{m^2} + 1} \over {{{\left( {x + m} \right)}^2}}} > 0\,\,\forall x \ne - m \cr
& \Rightarrow Ham\,\,so\,\,DB/\left( { - \infty ; - m} \right);\,\,\left( { - m; + \infty } \right)\,\,\forall m \cr} $$