a)∡AOB + ∡BOC +∡COD + ∡DOE +∡EOA = 360°
∡AOB=90° ; ∡COD=x+70° ; ∡DOE=x ; ∡AOE=2x+40° ; ∡BOC=∡COE=2x+70°
90°+ x+70° + x +2x+40° +2x+70°=360°
6x=360°-270°
6x=90° ⇒x=15°
b)
∡AOE=2·15°+40°=70°
∡MOE=∡AOE : 2 = 35° ⇒∡MOD= 35° + 15° = 50°
2. ON bis ∡BOC ⇒ ∡BON≡∡NOC
∡BOC=2·15°+70°=100° ⇒ ∡NOC=∡BOC : 2 =100° : 2 = 50°