<AOB+<BOC+<COD+<AOD=360°
<BOC=2•<AOB; <COD=<COA si <AOD=108°
<COA (sau <AOC) = <AOB+<BOC; deci in loc de <AOB+<BOC scriem <COA
=> <COA+<COD+108°=360°; dar <COA=COD
=> 2•<COA=360°-108°
<COA=252°:2
<COA=<COD=126°
<AOB+<BOC=<AOB+2•<AOB=3•<AOB=126°
=> <AOB=126°:3=42° si <BOC=2•42°=84°
R: <AOB=42°; <BOC=84°; <COD=126° si <AOD=108°
42°+84°+126°+108°=360°