How to make edge parallel to other edge?

I have two edges (non-parallel) and I want the first edge (active) to be parallel to the second one (blue color):

How would I do it?

The easiest way to do it would probably be to turn on face snapping, and just move it away from the surface once you got it aligned.

Someone is probably going to have a better method but this is what i usually do:

(note: Parts need to be separate objects)
Extrude the object into the other object.
Add boolean difference modifier to object you just extruded, set other object as target.
Apply boolean modifier.

Select a face aside the blue edge and add a custom transform, select the previous active edge and scale it to 0 on the custom transform axes needed.

But the active edge collapses into the point after the scaling on all axes:

Hmm, you know you can do this all in Edit Mode:

I used Normal Transform Orientation to extrude the faces.

Or do this:

Select this face, key SHIFT+7

Select face to manipulate, set View Transform Orientation, key S Z 0:

(I turned the view back so you can see the face is correct)

Just select the axis you want, View Depth is Z, so key S Z 0…

Keying something like S SHIFT+Z 0 means set X and Y axes to 0, leave Z alone.

Cheers, Clock.