a = 100
b = 50
c = 20
da = 0.002
db = 0.0008
dc = 0.0006
B = angle(a,b,c)
dB_a = (angle(a+da,b,c) - B)/da
dB_b = (angle(a,b+db,c) - B)/db
dB_c = (angle(a,b,c+dc) - B)/dc

ua = da/sqrt(3)
ub = db/sqrt(3)
uc = dc/sqrt(3)
uB = sqrt((dB_a*ua)^2 + (dB_b*ub)^2 + (dB_c*uc)^2)

k= 2
UB = k * uB

disp (['Indication du resultat: Beta = ' num2str(B) ' +/- ' num2str(UB,1) ' rad' ])