daca OX bisect ∡AOB rezulta ∡AOX=∡BOX=∡AOB/2
daca OY bisect∡COD rezulta ∡COY=∡YOD=∡COD/2
∡XOY= ∡XOB+∡BOC+∡COY
83=∡XOB+65+∡COY rezulta ∡XOB+∡COY= 83-65=18
∡AOB=2*∡BOX si ∡COD=2*∡COY
∡AOD= ∡AOB+∡BOC+∡COD= 2*∡BOX+65+2*∡COY=65 +2* (∡XOB+∡COY)=65+2*18=65+36=101 rezulta ∡AOD=101