∡AOB + ∡BOC+ ∡COD+ ∡DOA = 360°
∡AOB+ ∡BOC = 180 ⇒ ∡BOC = 180 - ∡AOB
∡AOB + ∡AOD =90 ⇒ ∡AOD = 90 - ∡AOB
∡AOB + 180 - ∡AOB + 3∡AOB +90 - ∡AOB=360
2∡AOB + 270 = 360
2∡AOB =360-270
2∡AOB =90
∡AOB = 90:2
∡AOB = 45° ⇒ ∡BOC=180-45=135°
∡AOD = 90-45=45°
∡COD = 3*45=135°
b) ∡AOB = ∡ AOD=45° ⇒ [OA bisectoarea ∡ BOD