sunt doua perechi de unghiuri opuse la varf:a) 2 si 4; 3 si 1; b)∡2 op la v. cu∡4⇒∡2≡∡4⇒m(∡2)=m(∡4)=54° m(∡1)+m(∡2)+m(∡3)+m(∡4)=360° 2m(∡1)+2m(∡2)=360° 2m(∡1)+2×54°=360° 2m(∡1)=360°-108° 2m(∡1)=252° m(∡1)=252°:2=126° c)∡1≡∡2⇒∡1≡∡2≡∡3≡∡4⇒m∡(1)=360°:4=90°
