Tứ giác ABCD có AD//CD , AB<CD ,AD=BC. Chứng minh ABCD là hình thang cân
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26 tháng 11 2022
1/nối AC
Do AB//CD=>BAC=ACD(so le trong)
Do AD//BC=>ACB=DAC(so le trong)
Xét ∆ABC và ∆ACD
ACB=DAC(chứng minh trên)
BAC=DAC(chứng minh trên)
AC chung
Vậy ∆ABC=∆CDA(g.c.g)=>AB=DC(cặp cạnh tương ứng)
AD=BC(cặp cạnh tương ứng)
và 
. 
và 
.
PG
2
9 tháng 12 2021
Xét tứ giác ABCD có
AB//CD
AD//BC
DO đó: ABCD là hình bình hành
Suy ra: AB=CD; AD=BC
YN
0
25 tháng 7 2017
AB = 5cm
=> BC = 12 - 5 = 7cm
=> CD = 12 - 7 = 5cm
=> AD = 12 - 5 = 7cm
Vì AB = CD, BC = AD, mà AB đối CD, BC đối AD
=> Tứ giác ABCD là hbh
NT
1
26 tháng 7 2019
Wave
| Cách chia động từ wave rất dễ, Bạn phải nhớ 3 dạng ở bảng đầu tiên để có thể chia động từ đó ở bất kỳ thời nào.Giờ bạn xem cách chia chi tiết của động từ wave ở bảng thứ 2 chi tiết hơn về tất cả các thì. |
Chia Động Từ: WAVE
| Nguyên thể | Động danh từ | Phân từ II |
| to wave | waving | waved |
| Bảng chia động từ | ||||||
| Số | Số it | Số nhiều | ||||
| Ngôi | I | You | He/She/It | We | You | They |
| Hiện tại đơn | wave | wave | waves | wave | wave | wave |
| Hiện tại tiếp diễn | am waving | are waving | is waving | are waving | are waving | are waving |
| Quá khứ đơn | waved | waved | waved | waved | waved | waved |
| Quá khứ tiếp diễn | was waving | were waving | was waving | were waving | were waving | were waving |
| Hiện tại hoàn thành | have waved | have waved | has waved | have waved | have waved | have waved |
| Hiện tại hoàn thành tiếp diễn | have been waving | have been waving | has been waving | have been waving | have been waving | have been waving |
| Quá khứ hoàn thành | had waved | had waved | had waved | had waved | had waved | had waved |
| QK hoàn thành Tiếp diễn | had been waving | had been waving | had been waving | had been waving | had been waving | had been waving |
| Tương Lai | will wave | will wave | will wave | will wave | will wave | will wave |
| TL Tiếp Diễn | will be waving | will be waving | will be waving | will be waving | will be waving | will be waving |
| Tương Lai hoàn thành | will have waved | will have waved | will have waved | will have waved | will have waved | will have waved |
| TL HT Tiếp Diễn | will have been waving | will have been waving | will have been waving | will have been waving | will have been waving | will have been waving |
| Điều Kiện Cách Hiện Tại | would wave | would wave | would wave | would wave | would wave | would wave |
| Conditional Perfect | would have waved | would have waved | would have waved | would have waved | would have waved | would have waved |
| Conditional Present Progressive | would be waving | would be waving | would be waving | would be waving | would be waving | would be waving |
| Conditional Perfect Progressive | would have been waving | would have been waving | would have been waving | would have been waving | would have been waving | would have been waving |
| Present Subjunctive | wave | wave | wave | wave | wave | wave |
| Past Subjunctive | waved | waved | waved | waved | waved | waved |
| Past Perfect Subjunctive | had waved | had waved | had waved | had waved | had waved | had waved |
| Imperative | wave | Let′s wave | wave |
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Nguyên thể Động danh từ Phân từ II to wave waving waved Bảng chia động từ Số Số it Số nhiều Ngôi I You He/She/It We You They Hiện tại đơn wave wave waves wave wave wave Hiện tại tiếp diễn am waving are waving is waving are waving are waving are waving Quá khứ đơn waved waved waved waved waved waved Quá khứ tiếp diễn was waving were waving was waving were waving were waving were waving Hiện tại hoàn thành have waved have waved has waved have waved have waved have waved Hiện tại hoàn thành tiếp diễn have been waving have been waving has been waving have been waving have been waving have been waving Quá khứ hoàn thành had waved had waved had waved had waved had waved had waved QK hoàn thành Tiếp diễn had been waving had been waving had been waving had been waving had been waving had been waving Tương Lai will wave will wave will wave will wave will wave will wave TL Tiếp Diễn will be waving will be waving will be waving will be waving will be waving will be waving Tương Lai hoàn thành will have waved will have waved will have waved will have waved will have waved will have waved TL HT Tiếp Diễn will have been waving will have been waving will have been waving will have been waving will have been waving will have been waving Điều Kiện Cách Hiện Tại would wave would wave would wave would wave would wave would wave Conditional Perfect would have waved would have waved would have waved would have waved would have waved would have waved Conditional Present Progressive would be waving would be waving would be waving would be waving would be waving would be waving Conditional Perfect Progressive would have been waving would have been waving would have been waving would have been waving would have been waving would have been waving Present Subjunctive wave wave wave ...BD3
7 tháng 9 2017Chứng minh rằng AK=KC,BI=ID
vì FE là đường trung bình hình thang nên FE//AB//CD
E, F là trung điểm của AD và BC nên AK=KC
BI=ID
( trong tam giác đường thẳng qua trung điểm của 1 cạnh, // với cạnh thứ 2 thì qua trung điểm cạnh thứ 3)7 tháng 9 2017Xét t/g ABC và t/g CDA có :
AC cạnh chung
AB = CD ( gt )
\(\widehat{A1}=\widehat{C1}\)( slt , AB // CD )
\(\Rightarrow\)t/g ABC = t/g CDA ( c-g-c )
\(\Rightarrow\)BC = AD
\(\widehat{A2}=\widehat{C2}\) và 2 góc này ở vị trí slt
\(\Rightarrow\)BC // AD
NN0