a/

Ta có: a⊥ c

           b⊥ c

=> Góc A = 90* (là điểm cắt của a  và c )

     Góc B= 90* (là điểm cắt của b và c )

Mà góc A và góc B là cặp góc trong cùng phía (1)

Góc A+ Góc B= 180*  (2)

Từ (1) và (2) ta có a // b

b/

Ta có a// b

=> Góc A4 và B là cặp góc trong cùng phía

=> \(\widehat{A4}+\widehat{B}=180\)

=> Góc A4= 180- 75

=> Góc A4= 105*

Vì góc A4 bù nhau vs A1

=> A4+ A1= 180*

=> A1= 180*- 105*

=> A1= 75*

Vậy góc A4= 105*

              A1= 75*

Thay số: \(\widehat{A4}+75=180\)

1. Quang/ brother/ walk/ movie theater/ moment.

=> Quang's brother is walking to the movie theater at the moment.

2. Mrs. Ba/ going/ buy/ some/ apples/ children.

=> Mrs.Ba is going to buy some apples for children.

3. I/ not/ hungry/ but/ thirsty/ like/ glass/ water.

=> I am not hungry but I am thirsty and I like a glass of water.

4. What/ you/ want/ me/ buy/ you?

=> What do you want to me buy for you?

5. look/ they/ drink tea/ and/ eat sandwiches over there.

=> Looking at! They are drinking tea and eating sandwichs over there.

1.There are some leaf on the table.                => leave 

2.What is the weather like in Liz country today?            => Liz's country

3.Lan goes to English club two a week.                 => twice 

4.They always aren't free on Sundays.         => be   

5.Hoa has  black round eyes.           => round black

6.Is usually it cold in winter?      => it usually 

7.That is my sister over there.She stands near the window.                 => She is standing 

8.Do you know how many teacher your school has?        => any

9.Here are paddy behind my school.          => Here paddy are

10.My sister is going to the market with my.             => me

11.Mr.Minh rides his bike to work at the moment.       => is riding

12.How many homework does Lan have every day?              => much

13.A lot of my friends play soccer,but not much of them play tennis.          => any

14.Are they many students in your class?      => there

15.Our classroom in on the three floor.                 => third 

1. Nga has some books.

(-) Nga doesn't have any books.

(?) Does Nga have any book?

2. Nam and Thu have some tea

(-) Nam and Thu don't have any tea.

(?) Do Nam and Thu have any tea?

3. He wants some milk.

(-) He doesn't want any milk.

(?) Does he want any milk?

4. There are some apples.

(-) There aren't some apples.

(?) Are there any apple?

5. There is some meat.

(-) There isn't any meat.

(?) Is there any meat?

6. I feel thirsty now.

(-) I don't feel thirsty now

(?) Do you feel thirsty now?

7. He likes some coffee.

(-) He doesn't like any coffee.

(?) Does he like any coffee?

8. She can stay here.

(-) She can't stay here

(?) Can she stay here?

9. I'm hungry

(-) I am not hungry 

(?) Are you hungry?

10. They want some help.

(-) They don't want any help

(?) Do they want any help?

Gọi tia phản xạ là IR

Ta có: Góc phản xạ luôn bằng góc tới

=> Góc phản xạ là 30*

Ta kẻ thêm một đường Ox // AB

=> Góc BAO và góc AOx là cặp góc trong cùng phía

=> BAO+ AOx= 180

=> 75* + AOx= 180*

=> AOx= 180*- 75*

=> AOx= 105*

Từ hình vẽ ta có:

AOC+ AOx+ COx= 360*

=> 105*+ 105*+ COx= 360*

=> COx= 150*

Mà COx và OCD là cặp góc trong cùng phía (1)

      COx+ OCD= 180* (2)

Từ (1) và (2) ta suy ra Ox // CD

Ta có: AB // Ox

           CD// Ox

=> AB// CD ( theo tính chất từ vuông góc đến song song)

Vậy AB// CD

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