2. Ko'pburchak ichki burchaklarining yig'indisi. Qavariq n burchak ichki burchaklarining yig'indisi 180° (n — 2) ga teng, bunda n — tomonlar soni. 1. Qavariq ko'pburchakning ichki burchaklari yig'indisi 180° ga karrali bo'ladi. 2. Qavariq ko'pburchakning har bir burchagi 180° dan kichikdir. 3. Ko'pburchak burchaklari yig'indisi to'g'risidagi teorema qavariq bo'lmagan ko'pburchaklar uchun ham o'rinli. 3. Ko'pburchak tashqi burchaklarining yig'indisi. T a ' r i f . Ko'pburchakning berilgan uchidagi tashqi burchagi deb, uning shu uchidagi ichki burchagiga qo 'shni burchakka aytiladi. Qavaruq n burchakning har bir uchidan bittadan olingan tashqi burchaklarining yig'indisi 360° ga teng. I sbot. Ko'pburchakning har qaysi uchida bittadan tashqi burchak yasaymiz. Ko'pburchak ichki burchagi va u bilan qo'shni bo'lgan tashqi burchagi yig'indisi 180° ga teng (10-rasm). Shu sababli barcha ichki va har bir uchidan bittadan olingan tashqi burchaklarining yig'indisi 180° n ga teng. Ammo ko'pburchakning hamma ichki burchaklarining yig'indisi 180°(n-2) ga teng. U holda har qaysi uchidan bittadan olingan tashqi burchaklarning yig’indisi 180°n - 180°(n – 2) = 180°n – 180°n + 360° = 360° bo’ladi.
4. Yangi mavzuni yoritish va Yangi mavzuni mustahkamlash: --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------