\(\perp\) d, CE...">
K
Khách

Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.

13 tháng 2 2016

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7 tháng 3 2017

CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCGCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC

5 tháng 8 2017

A/ Theo giả thiết ta có:DA=BA;AE=AC\(\Rightarrow\) DC=BE

Vì tam giác BDA là tam giác vuông cân\(\Rightarrow\)góc A=90 độ\(\Rightarrow\) DC vuông góc vs BE

B/ Áp dụng định lý Pi-ta-go cho tam giác BAD vuông tại A:BD2=BA2+AD2

                                                                               ACE vuông tại A:CE2=AC2+AE2

                                                                                ADE vuông tại A:DE2=DA2+AE2

                                                            BAC vuông tại A:BC2=AB2+AC2

                                          Từ trên suy ra:BD2+CE2=BC2+DE2

C/Xét tam giác BAC và DAE:DA=BA

                                        BA=AE

                                        GÓC BAC=GÓC DAE=90

                             \(\Rightarrow\) Tam giác BAC=DAE(c-g-c)

                             \(\rightarrow\) BC=DE(2 cạnh t/ứ)

                             \(\rightarrow\) góc CBA=góc AED(t/ứ)

                              mà 2 góc nàm vị trí so le trong\(\Rightarrow\)BC song song DE

                            \(\rightarrow\) góc BCE+góc CED=180 ĐỘ(2 góc phía trong cùng phía)

                             mà góc DCE=góc BEC(TAM GIÁC cae VUÔNG CÂN)

                             \(\Rightarrow\) Góc BCD=góc BED

                              MÀ góc BCD=CDE(so le trong)

                             \(\Rightarrow\) góc ADE=góc AED\(\Rightarrow\) TAM GIÁC ADE vuông cân tai E

                             mà ta có AI(IK cắt DE ở I)LÀ đường trung trực của tam giác

                            \(\rightarrow\) AI cx là đg trung tuyến của ADE

                            \(\Rightarrow\) I là trung điểm của DE

                           MÀ ta lại có BC=DE(cm phần trên rồi)

                          \(\Rightarrow\) k là trung điểm của BC

(ko bít vẽ hình)

6 tháng 8 2017

Sai rồi bạn ơi, đề bài cho là \(\widehat{A}< 90\) độ.

19 tháng 3 2017

A B C D E M d

a)  Ta có: \(\widehat{DAB}+\widehat{CAE}=180^0-\widehat{BAC}=90^0\)(1)

               \(\widehat{DAB}+\widehat{DBA}=180^0-\widehat{BDA}=90^0\)(2)

Từ (1) và (2) \(\widehat{DAB}+\widehat{CAE}=\widehat{DAB}+\widehat{DBA}\Rightarrow\widehat{CAE}=\widehat{DBA}\)

Xét\(\Delta DAB\)\(\Delta ECA\)có:\(\hept{\begin{cases}\widehat{BDA}=\widehat{AEC}=90^0\\AB=AC\\\widehat{DBA}=\widehat{CAE}\end{cases}\Rightarrow\Delta DAB=\Delta ECA}\)(cạnh huyền góc nhọn)

\(\Rightarrow\hept{\begin{cases}EC=AD\\BD=AE\end{cases}\Rightarrow BD+EC=AD+AE}=DE\) 

1 tháng 4 2018

bn tham khảo link dưới nha!

https://olm.vn/hoi-dap/question/1167250.html

CHÚC BN HỌC TỐT!!!!!

3 tháng 4 2018

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