a,Do tam giác ABC là tam giác cân => AB = AC

Do AB = AC => AD = BD = AE = CE

Xét tam giác ABE và tam giác ACD có:

                       AB = AC (ở trên)

                       góc DAE là góc chung

                       AD = AE

=> tam giác ABE = tam giác ACD

b, Do tam giác ABE = tam giác ACD ( câu a)

=> BE = CD

c, nhác quá, bài này dài, tự làm đê

a.

\(\frac{2}{-7}< 0\)

\(0< 0,25\)

\(\Rightarrow\frac{2}{-7}< 0,25\)

\(\Rightarrow y< x\)

b.

\(-\frac{3}{101}< 0\)

\(0< \frac{1}{97}\)

\(\Rightarrow\frac{-3}{101}< \frac{1}{97}\)

\(\Rightarrow x< y\)

c.

\(\frac{4}{-3}< 0\)

\(0< \frac{-1}{-103}\)

\(\Rightarrow\frac{4}{-3}< \frac{-1}{-103}\)

\(\Rightarrow x< y\)

a, Xét Δ ABK và Δ CDK có :

KB = KD ( gt )

AK = KC ( do K là trung điểm AC)

\(\widehat{AKB} = \widehat{CKD}\) ( hai góc đối đỉnh )

=> Δ ABK = Δ CDK ( c - g-c )

b, DO Δ ABK = Δ CDK ( cm trên )

=> \(\widehat{ABK} = \widehat{KCD} \) ( hai góc tương ứng )

mà hai góc này nằm ở vị trí so le trong => AB // CD

phần c mk ko bt lm sorry nha (hình bn tự vẽ nha)

1, Mount Everest is ……​the………… highest mount in the wall. 
2, I would like to buy ………a……… new clothes but I haven’t ……the………… money. 
3, Are there ………a……… letters for me today? 
Yes, there is only one from New York. 
4, I have got ……a………… little money left, let’s have dinner in …………the…… restaurant. 
5, My mother goes to …the…………… church in …………the…… morning and …the…………… afternoon goes to visit ………the……… friends. 
6, It takes me half ……a………… hour to get to work by ………a……… bus. 
7, What does ………the……… post office sell apart from stamps? 
8, I want to buy …an…………… envelope and …………the…… fifty thousand dong phone card. 
9, Viet would like to send his sister in ………the……… USA ………a……… letter. 
10, Go along this road and take ………the……… second turning on ………the……… left. 

Điền a/an/the hoặc some :

1, Mount Everest is ……the……… highest mount in the wall. 
2, I would like to buy ………some……… new clothes but I haven’t ………the……… money. 
3, Are there ………some……… letters for me today? 
Yes, there is only one from New York. 
4, I have got ………a……… little money left, let’s have dinner in ……the………… restaurant. 
5, My mother goes to ………the……… church in …………the…… morning and ………the……… afternoon goes to visit ………the……… friends. 
6, It takes me half ………a……… hour to get to work by ………ko dien……… bus. 
7, What does ………the……… post office sell apart from stamps? 
8, I want to buy ………an……… envelope and ………the……… fifty thousand dong phone card. 
9, Viet would like to send his sister in ……the………… USA ……a………… letter. 
10, Go along this road and take ……the……… second turning on ………the……… left. 

Ta có: \(B=\frac{\frac19-\frac17-\frac{1}{11}}{\frac49-\frac47-\frac{4}{11}}+\frac{0,6-\frac{3}{25}-\frac{3}{125}-\frac{3}{625}}{\frac45-0,16-\frac{4}{125}-\frac{4}{625}}\)

\(=\frac{\frac19-\frac17-\frac{1}{11}}{4\left(\frac19-\frac17-\frac{1}{11}\right)}+\frac{\frac35-\frac{3}{25}-\frac{3}{125}-\frac{3}{625}}{\frac45-\frac{4}{25}-\frac{4}{125}-\frac{4}{625}}\)

\(=\frac14+\frac{3\left(\frac15-\frac{1}{25}-\frac{1}{125}-\frac{1}{625}\right)}{4\left(\frac15-\frac{1}{25}-\frac{1}{125}-\frac{1}{625}\right)}\)

\(=\frac14+\frac34=\frac44=1\)

a: Xét ΔDBI vuông tại D và ΔECI vuông tại E có

BI=CI

\(\widehat{B}=\widehat{C}\)

Do đó: ΔDBI=ΔECI

b: Tacó: AD+DB=AB

AE+EC=AC

mà AB=AC

và DB=EC

nên AD=AE
hay ΔADE cân tại A

a,\(\dfrac{3}{5}+\dfrac{2}{7}=\dfrac{31}{35}\)

b,\(\dfrac{-4}{3}:\dfrac{2}{15}=\dfrac{-60}{6}=-10\)

c,\(\dfrac{3}{7}.\dfrac{2}{9}+\dfrac{7}{9}.\dfrac{3}{7}=\dfrac{3}{7}.\left(\dfrac{2}{9}+\dfrac{7}{9}\right)=\dfrac{3}{7}\)

d,\(\left(\dfrac{-2}{3}\right)^3.9^2+\left(\dfrac{-3}{4}\right)^2.32\)

\(=\dfrac{\left(-2\right)^3}{3^3}.3^4+\dfrac{\left(-3\right)^2}{4^2}.2^5\)

\(=\left(-8\right).3+\dfrac{3^2}{4^2}.2^5\)

\(=\left(-24\right)+2.9\)

\(=\left(-24\right)+18\)

\(=-6\)

a,