Question 1097591
The expression {{{(m^2-2m-3)/ (m^2-10m+21)}}}
has no value when {{{m^2-10m+21=0}}} ,
and since {{{m^2-10m+21=(m-7)(m-3)}}} ,
{{{m^2-10m+21=(m-7)(m-3)=0}}} if and only if {{{m=7}}} or {{{m=3}}} .
Those values of {{{m}}} are excluded.
 
{{{m^2-2m-3=(m+1)(m-3)}}} ,
so for {{{m<>3}}} , {{{(m^2-2m-3)/ (m^2-10m+21)=(m-7)(m-3)/((m+1)(m-3))=(m-7)/(m+1)}}} .