Snapping does work, but it has to be in 2 constrained moves, I think.
Snap set to 'Vertex' and 'Active'
G X, and then G Y to the relevant vertices, with the snap active.
The first move could be G G, a slide, no snap, as far as it will go.
It's still there, just the name is changed :).
Now it's called Align to Vertex Normal ✓
When setting up the constraint, change Mix to Add.
Otherwise the triangles won't line up later.
You can add the constraint to other objects using Object > Constraint > Copy Constraints. Just make sure, the constraint isn't on the circle itself :).
This pretty much exactly what the Spin tool is for ..
In an orthogonal view of the circular arc you want to create, put the 3D cursor at the center of the new part-circle, select the vertex you want to extrude around it, and invoke the tool.
In your case, you might ShiftS snap the cursor to the two selected endpoints of the bevel, so it's exactly between ...
You can apply a bezier curve to a plane using the knife project tool.
Heres my process:
As a separate object, make the curve that you want (mine is pretty bad for a door):
Next, covert the curve to a mesh using the "convert to" tool:
Now, select first the curve mesh, and then the plane, go into edit mode, and do knife project:
The knife project does it ...
Assuming you are using Blender 2.8, just follow the tutorial until the desired vertices are selected, then do the following:
Press Ctrl+B (to activate the Bevel Tool)
Press V (to make the tool act on vertices)
Drag your mouse outwards until you get the same shape as the one in the tutorial.
Note that, whenever you've selected a tool (such as the bevel tool)...
I can make 3 examples of 3 different ways of doing this (and there can be many more).
1 - Vertex parent: select 3 vertices of the eyelid, then in object mode select the eyelash; shift select the eyelid and press Ctrl P (choose vertex triangle), so that eyelashes will follow any movement of the 3 choosen vertices.
2 - Drivers: set a shape key for the ...