Qua C dựng đường thẳng t song song với By

⇒ Ct //A\(x\) Vì trong cùng một đường thẳng nếu  hai đường thẳng cùng song song với đường thẳng thứ ba thì song song với nhau.

\(\widehat{ACt}\) + \(\widehat{CAx}\) = 180⁰ (hai góc trong cùng phía)

⇒ \(\widehat{ACt}\) = 180⁰ - 140⁰ = 40⁰

\(\widehat{yBC}\) =  \(\widehat{BCt}\) = 20⁰ (hai góc se trong)

mặt khác ta có: \(\widehat{ACB}\) =  \(\widehat{ACt}\)  + \(\widehat{BCt}\)

               ⇒ \(\widehat{ACB}\) = 40⁰ + 20⁰ 

                   \(\widehat{ACB}\) = 60⁰

Cô ơi cho em hỏi tại sao mình phải chứng minh Ct //Ax

Lời giải:
a.

Ta thấy $\widehat{BAE}=\widehat{DCE}$ mà 2 góc này ở vị trí so le trong nên $AB\parallel CD$

$\Rightarrow \widehat{ABE}=\widehat{EDC}$ (so le trong)

Xét tam giác $ABE$ và $CDE$ có:

$AB=CD$

$\widehat{BAE}=\widehat{DCE}$ (gt)

$\widehat{ABE}=\widehat{CDE}$ (cmt) 

$\Rightarrow \triangle ABE=\triangle CDE$ (g.c.g)

$\Rightarrow AE=CE; BE=DE$ nên $E$ là trung điểm $AC, BD$

b. Hai tam giác này không bằng nhau.

c. Xét tam giác $ACD$ và $CAB$ có:
$AC$ chung

$CD=AB$

$\widehat{ACD}=\widehat{CAB}$ 

$\Rightarrow \triangle ACD=\triangle CAB$ (c.g.c)

$\Rightarrow \widehat{CAD}=\widehat{ACB}$

Mà 2 góc này ở vị trí so le trong nên $AD\parallel BC$

Pháp

@Duy Nguyễn Văn Duy sai rồi bạn ơi , pháp nước đó ở gần đức mà .

Lời giải:

$2x^2+2y^2=5xy$

$\Leftrightarrow 2x^2+2y^2-5xy=0$

$\Leftrightarrow (2x^2-4xy)-(xy-2y^2)=0$

$\Leftrightarrow 2x(x-2y)-y(x-2y)=0$

$\Leftrightarrow (x-2y)(2x-y)=0$

$\Leftrightarrow x=2y$ hoặc $2x=y$

Do $0< x< y$ nên $2x=y$

Khi đó: $E=\frac{x+y}{x-y}=\frac{x+2x}{x-2x}=\frac{3x}{-x}=-3$

1. No one in Na's family is as hard as her.

Na is among............the hardest in her family...........................................................................
2. They prefer cooking to washing the dishes.

They like cooking better than washing the dishes 

They would rather..........cook than wash the dishes............................................................................
3. Mr Tan has more days off than Mr Long.

Mr long does........more days than Mr Tan....................................................................

Mr Long............has fewer day off than Mr Tan............................................................................
4. They couldn't play badminton because of the windy weather.

The windy weather prevented.......them from playing badminton.....................................................
5. He speaks more fluently than his friends

He is........a more fluent speaker than his friends................................................................................
6. This is the worst film we have ever seen.

We have never......a worse film than this film.................................................................
7. We are quick runners.

We run...........quickly................................................................................
8. How a big the tree is!

What...............a big tree.......................................................
9. This magazine has a lot of information.

There........is a lot of information in this magazine.................................................................
10. We can play the gitar very well

We are capable of playing the guitar
11. Swimming in the summer is good for your health.

It's.........................good for your health to swim in the summer..............................................

Lời giải:

a. $x(\frac{4}{5}x-1)(0,1x-10)=0$

$\Rightarrow x=0$ hoặc $\frac{4}{5}x-1=0$ hoặc $0,1x-10=0$

Nếu $\frac{4}{5}x-1=0$

$\Rightarrow x=1: \frac{4}{5}=\frac{5}{4}$

Nếu $0,1x-10=0$

$\Rightarrow x=10:0,1=100$

Vậy $x=0; \frac{5}{4}; 100$

b.

$(\frac{1}{4}x-1)-(\frac{5}{6}x+2)-(1-\frac{5}{8}x)=0$

$(\frac{1}{4}x-\frac{5}{6}x+\frac{5}{8}x)-(1+2+1)=0$

$\frac{1}{24}x-4=0$

$x=4: \frac{1}{24}=96$

y nghi cua chien thang lich su dien bien phu

Cấu hình X: 1s²2s²2p¹ 

=> X có 5e => STT ô thứ 5, chu kì 2, nhóm IIIA