radial lines as stone arch

gosh, so many different ways to do that.
need to make some assumptions here, I am guessing that the tangent to the arc midpoint is horizontal. then, do you want a certain number of "segments" or a specific angle repeated?
if a certain number of segments is what serves your purpose, play with the divide command. let it create nodes on the outer arc, and draw line segments from node to center of the arc. then trim back to the inner arc.
if it is an angle you want to repeat, start at the outer midpoint, draw back to the center, trim back to the inner arc, create a polar array based on your angle, and mirror.
good?

Thanks for your explanation. I will try this evening, but i yet see how to do.
I will confirm to you, tomorrow morning.
Thanks. Le Nordiste

I tried the first method, PERFECT, if i except the number of segments - 64 on a quarter of circle- next lesson i will try the second method and make a comparison between the two drawing.
Thanks Roy. Le Nordiste

:)