You can use the constraints to do it. The snap options don't show up as tangent when you move near them.
If it was the other way round and you had the arc in, you click and hold the mouse button and drag a line off from the arc and it'll show up as tangent

I found that it works (well, in Shark v10 anyway, nearest convenient PC because IMSI's Shark Pro 12 license now restricts to one installation) using the logicursor's determination of "on" the line to be the tangent point. I verified it by drawing lines from the arc's centre to its ends, obviously they're the radius. I drew a line from the centre to the "vertex" point that the logicursor determines as the intersection/tangent of line and circle, scaled it larger so that it overshoots centre and tangent, trimmed it back using one of the radial lines and the tangent line, then verified by comparing that it's the same radius length. I'll post a graphic if you need it?

You must be right, but I can't think why it works when it does - which it does some of the time. It must have something to do with the proximity detection for 'on the curve'. Do I remember you having an affection for retro caravans/trailers Mike?

Tried it in v10 and it doesn't label tangent either. There's the click and hold option. So looking at what you have you would maybe need to put a point in where you would terminate the line.

A little vid attached shows it

Yea it depends which way round you do it all. The tangent shows up as a second point of a line. So click and drag, approach the arc and you'll get a tangent pop up.

Ah see what you mean, sorry I have been using the set up of the op. But I don't see a reason why you can't do it your way yeah. Just thought they wanted to define the end points first

Nice find MPSchmied!!! I've never even tried the 3 Point Arc. I thought it was the same as Start, End, On Arc.

So it does indeed make an arc tangent to a line! What a time saver this will be over fully constraining any sketch that need a tangent arc!

Mike...