a) Xét \(\Delta ABC\) có:

Góc ngoài tại đỉnh A = \(\widehat{B}+\widehat{C}\)

\(\Rightarrow\widehat{A_1}+\widehat{A_2}=2\widehat{B}\) ( Góc A₁, góc A₂ là góc được tạo ra bởi tia Ax)

Mà \(\widehat{A_1}=\widehat{A_2}\)

\(\Rightarrow2\widehat{A_2}=2\widehat{B}\Rightarrow\widehat{A_2}=\widehat{B}\)

Mà 2 góc này ở vị trí so le trong

=> Ax // BC

b) Xét \(\Delta ABC\) có: \(\widehat{B}=\widehat{C}\)

=> \(\Delta ABC\) cân

=> AH là đường cao đồng thời là tia phân giác góc A

=> AH là tia phân giác \(\widehat{BAC}\)

- Tiếng là âm thanh, mỗi lần nói là một tiếng. Tiếng có nghĩa hoặc không có nghĩa

- Từ thì có nghĩa. Tiếng câu tạo nên từ

Đề đơn giản thế này

Ta có: \(\dfrac{1}{2}=\dfrac{30}{60}\)

\(\dfrac{1}{3}=\dfrac{20}{60}\)

Số hữu tỉ giữa \(\dfrac{1}{2}\) và \(\dfrac{1}{3}\) là \(\dfrac{29}{60}\)

Quy đồng lên

1. She goes to the movies once a month

=> How often does she go to the movies?

2. Yes . He's from England

=> Is he from England?

3. Her mother is going to the market now

=> Where is her mother going to now?

4. The mekong river is the longest river in Vietnam

=> Which is the longest river in Vietnam?

5. We have a lot of beautiful flowers

=> How many beautiful flowers do you have?

6. They speak French

=> Which language do they speak?

8. She is japanese

=> What is she nationality?

\(\widehat{x'Oy}\) kề bù với \(\widehat{xOy}\)

\(\Rightarrow\)\(\widehat{x'Oy}\) + \(\widehat{xOy}\) = 180⁰

\(\Rightarrow\)\(\widehat{x'Oy}\) = 180⁰ - 30⁰

\(\Rightarrow\)\(\widehat{x'Oy}\) = 150⁰

\(\widehat{x'Oy'}\) kề bù với \(\widehat{x'Oy}\)

\(\Rightarrow\)\(\widehat{x'Oy'}\) + \(\widehat{x'Oy}\) = 180⁰

\(\Rightarrow\)\(\widehat{x'Oy'}\) = 180⁰ - 150⁰

\(\Rightarrow\)\(\widehat{x'Oy'}\) = 30⁰

Vậy số đo góc \(\widehat{x'Oy'}\) là 30⁰

Xét \(\left\{{}\begin{matrix}AF\perp CD\\BE\perp CD\end{matrix}\right.\)

\(\Rightarrow\) AF // BE

\(\Rightarrow AB=FE\)

\(\Rightarrow FE=6cm\)

Xét hình thang ABCD cân

=> BC = AD; \(\widehat{C}=\widehat{D}\)

Xét tam giác vuông AFD và tam giác vuông BED có:

BC = AD

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

\(\Rightarrow\Delta AFD\:=\Delta BEC\) ( cạnh huyền - góc nhọn)

=> DF = EC ( 2 cạnh tương ứng)

=> DF = EC = \(\dfrac{DC-FE}{2}=\dfrac{20-6}{2}=7cm\)

Ta có: AB + BC + CA + AD = 76 cm

=> BC = AD = (76 - 6 - 20) : 2 = 25 cm

Xét tam giác vuông AFD có: \(AD^2=AF^2+FD^2=674\)

\(\Rightarrow AD=\sqrt{674}cm\)

I love school. I'm really interested...(1).in.... English and math. I often get....(2)good..... marks at school. I sometimes...(3).play... volleyball with my classmates in the afternoon. We like....(4)sports...... very much especially volleyball

1. Sister/ my/ is / live/ going/ country/ the/ to/ in

=> My sister is going to live in the country

2. Is/ phone/ what/ Tom/ you/ time/ going/ tonight/ to?

=> What time is Tom going to phone you tonight?

3. Going/here/ how/ friends/ are/ stay/ your/ long / to?

=> How long are your friends going to stay here?

4. To/are/ wear/ what/ the/ going/ you / party/ at?

=> What are you going to wear at the party?

5. New/ next / my/ give/ to/ week/ going/ mother/ bicycle/ is/ me/ a

=> My mother is going to give me a new bicycle next week

A = -17 + | 2x - 5 |

Ta có: | 2x - 5 | \(\ge\) 0

=> A \(\ge\) -17

Dấu " = " xảy ra khi: 2x - 5 = 0

=> 2x = 5

=> x = 2,5

Vậy GTNN của A là -17