có tôi lớp 8 đ

9

a)tg OBD và Tg ECO có

g OBD = g ECO (tg ABC cân tại A )(1)

g BOD =gOEC (gt)(2)

từ (1)và (2) => Tg OBD đồng dạng Tg ECO

ð OB/EC=BD/CO=>OB*CO=EC*BD

Mà OB = CO => OB bình =EC*BD

b)ta có g DOE =180 độ -(g BOD +g EOC)

=180 độ-(g OEC +g COE)

=180độ -(180 độ -g OCE )

=g OCE =g BCA =const (3)

c) Theo câu a :Tg OBD đồng dạng Tg ECO => OD/EO=BD/CO=>OD/EO=BD/BO

=>OD*BO= EO*BD=>EO/OB =OD/BD (4)

Mặt khác :từ (3) =>g DOE =g OBD (5)

Từ (4) và (5) => tg EOD đồng dạng tg OBD

a-b+c+3abc

=a-b+c+3abc+3ab+3ab-3ab-3ab

=(a-b)+c+3ab(a-b+c)

=(a-b+c)[(a-b)-(a-b)c+c]+3ab(a-b+c)

=(a-b+c)(a+b+c-ab-ac+bc)

Đọc hiểu và trả lời câu hỏi.

Last Sunday, Lan didn't go to school, but she went to her friend's birthday party. She got up early in the morning, went to the shop, and bought some gifts and flowers. Then, she went to her friend's house. At the party, she ate a lot of cakes and drank soft drink. She danced beautifully, sang many songs, and told a lot of interesting stories. All her friends were there too. They played many games such as hide and seek, skipping rope and cards. They were very happy and enjoyed themselves a lot. Finally, the party came to an end. They said goodbye to each other and went home late in the the evening.

Did Lan go to school yesterday?