Calculator for determining moment arm

[dbasmb]

I guess my trig and geometry are too old to figure this out. I would like an expression for the moment arm given a fixed point. So, given a point (z,-w) with a line going through that point, what is the distance from the origin, perpendicular to the line when the angle (Theta) of the line goes from zero degrees (parallel to the x axis) to 90 degrees (parallel to the y axis).

Seems easy but my 72 years are wearing thin.

Thanks for the help.