a: Xét ΔCDA vuông tại A và ΔCBA vuông tại A có

CA chug

DA=BA

Do đó:ΔCDA=ΔCBA

b: Ta có: ΔCDB cân tại C

mà CA là đường cao

nên CA là đường phân giác

c: Xét ΔCEI vuông tại E và ΔCFI vuôg tại F có

CI chung

\(\widehat{ECI}=\widehat{FCI}\)

Do đó:ΔCEI=ΔCFI

Suy ra: CE=CF

Xét ΔCDB có CE/CD=CF/CB

nên EF//DB

C D B B C A A D C

do

to be

were waiting

went-wouldn't be

were

smoking

is always leaving

to study

haven't spoken

arrive

1, If we recycled, we will save natural resources

2,If you don't be careful, you will be fall over rocks

3,If you work too much, you will feel tired

4,If you are careless, you will broke the vase

5,If Ha has work to hard, she can pass the exam

b)

1,If I knew the answer, I could give you

2,If you chose that job, you would pay for it

3, If Mrs Green had money, she could afford the house

4,If you had a pen, you could written down the address

5,If she was a president, she would change the law

c)

1, If If Jerry had understood the lesson, he would have answered

2,If Carol hadn't studied, she would have answered

3,If he had worked hard, he wouldn't have been fired

4,If I had been stucked in the traffic jam, I wouldn't have been late

5,If he hadn't gone out in the rain last night, he wouldn't have had a flu

Lời giải:
Bổ sung điều kiện $x$ nguyên.

Ta có:
$2x+7\vdots x-2$

$\Rightarrow 2(x-2)+11\vdots x-2$

$\Rightarrow 11\vdots x-2$
$\Rightarrow x-2\in \left\{1; -1; 11; -11\right\}$

$\Rightarrow x\in \left\{3; 1; 13; -9\right\}$

\(\Leftrightarrow\left(x-2021\right)\left(x-5\right)-\left(x-2021\right)=0\\ \Leftrightarrow\left(x-2021\right)\left(x-6\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=2021\\x=6\end{matrix}\right.\)

48,6phút:9+9,54phút

5,4phút+9,54phút

14,94phút

   [  48 phut 36 giay : 9  ]   +  9,54 phut                                                                                                                                                         =    5phut  24 giay              + 9,54   phut                                                                                                                                                               =    5,4  phut                       + 9,54 phut                                                                                                                                                               =    14,94 phut                                                           

   48 phút 36 giây : 9 + 9,54 phút

=  5 phút 24 giây + 9,54 phút

= 5,4 phút + 9,54 phút 

= 14,94 phút

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