Sana: 201 y. Mavzu: ko'pburchaklar darsning maqsadi

2. Trapetsiya. To'rtburchaklarning burchaklari yoki qarama-qarshi tomonlarining o'zaro joylanishiga qarab ular turli sinflarga ajtratiladi. Shu sinflardan eng soddasi — trapetsiya bilan tanishamiz.
To'rtburchakda ikki juft qarama-qarshi tomonlari bor. Shunday to'rtburchaklar mavjudki, ularda bir juft qarama-qarshi tomonlari parallel to'g'ri chiziqlarda yotishi mumkin. Masalan, l₁, l₂ parallel to'g'ri chiziqlar-ning har biridan ikkitadan nuqta olib, ularni o'zaro tutashtirsak (13-rasm), ABCD yoki KLMN to'rtburchaklarning bir juft qarama-qarshi tomonlari parallel bo'ladi.
T a ' r i f . Ikkita tomoni parallel, qolgan ikki tomoni parallel bo’lmagan to'rtburchak trapetsiya deb ataladi.
Trapetsiyaning parallel tomonlari uning asoslari, parallel bo'lmagan tomonlari esa yon tomonlari deb ataladi. Trapetsiyaning asoslari yotgan to'g'ri chiziqlar orasidagi masofa trapetsiyaning balandligi deyiladi (14-rasm). Trapetsiya asoslariga perpendikular bo'lgan har qanday kesma, uning balandligi sifatida olinishi mumkin, chunki parallel to'g'ri chiziqlar nuq-talari orasidagi masofalar o'zaro teng.
Teorema: Agar to’rtburchak biror qo’shni ikki burchagining yig’indisi 180^o bo’lsa, bunday to’rtburchak trapetsiya bo’ladi.
4. Yangi mavzuni yoritish va Yangi mavzuni mustahkamlash:
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