The length of the perpendicular from the point \( (1,-2,5) \) on the line passing through \( (1,2,4) \) and parallel to the line \( x+y-z=0=x-2y+3z-5 \) is:
\( \dfrac{\sqrt{21}}{2} \)
\( \sqrt{\dfrac{9}{2}} \)
\( \sqrt{\dfrac{73}{2}} \)
\( 1 \)