Given rational expression is
[tex]\frac{-12d-1}{10d+5}[/tex]
The given rational expression is undefined when
[tex]\begin{gathered} 10d+5=0 \\ 10d=-5 \\ d=-\frac{1}{2} \end{gathered}[/tex]
Hence, the value of d for which the rational expression is undefined is 0.5
