daniel Mentrard

La longueur  L de l'arc vaut:  L = α x r 

Source : Daniel Mentrard
http://dmentrard.free.fr/GEOGEBRA/
Adaptation: JM Delley
http://math.bibop.ch

O = (6.90934383371237, 6.10764927214219)
r = 3.5 (slider from 2 to 6, step 0.25)
c = Circle(O, r)
A = Point(c)
α = 1.3089969389957472 rad (slider from 0 to 6.19591884457987, step 0.08726646259971647)
B = Rotate(A, α, O)
β = Angle(A, O, B)
a = Segment(O, A)
b = Segment(O, B)
d = CircleArc(O, A, B)
αr: α * 3.1416 / 180 / °
T1: αr + ""
T2: "  L  =" + αr + "x" + r + "=" + d
e = AngularBisector(A, O, B)
C = Point(e)
f = Circle(O, C)
T4: "donc \,\, α \,\, en \,\, radians \,\,  vaut: \, \, " + (LaTeX[α]) + "    \frac{ π }{180° }  = " + (LaTeX[αr]) + " rad"