2 she had got the price of the contest, she would be happy now

3 I had gone to the concert last night ,I would be tired

4 John had finished all his homework, he could see a movie now

5 we had listened to my mother, we wouldn't be in trouble right now

Ex5

1 you arrive at the offcie earlier than I do, please turn on the air-conditioner

2 Were it not snowy, the children would go to school

3 he not died so young, he would be a famous musician

4 Were I you, I would take care of my car

5 not very bad-tempered, his wife would give him soon are marrage

6 Had she not got married at such an early age, he would be at university

to work

working

Lời giải:

a.

Tứ giác $ADME$ có 3 góc vuông: $\widehat{D}=\widehat{A}=\widehat{E}=90^0$ nên là hình chữ nhật.

b. 

Vì $ADME$ là hcn nên $AM=DE$

$MD\perp AB, AB\perp AC\Rightarrow MD\parallel AC$. Áp dụng định lý Talet:

$\frac{BD}{DA}=\frac{BM}{MC}=1\Rightarrow BD=DA\Rightarrow D$ là trung điểm $AB$

Tương tự thì $E$ là trung điểm $AC$

$\Rightarrow DE$ là đường trung bình của tam giác $ABC$ ứng với cạnh $BC$

$\Rightarrow AM=DE=\frac{BC}{2}=\frac{\sqrt{AB^2+AC^2}}{2}=\frac{\sqrt{6^2+8^2}}{2}=5$ (cm)

c.

$S_{AMB}=\frac{BM}{BC}S_{ABC}=\frac{1}{2}S_{ABC}=\frac{1}{2}.\frac{AB.AC}{2}=\frac{6.8}{4}=12$ (cm²)

Điểm H ở đây có vẻ không có giá trị lắm.

Hình vẽ:

\(21_{10}=10101_2\)