a) Om là tia phân giác \(\widehat{xOz}\left(gt\right)\)
\(\Rightarrow\widehat{mOz}=\dfrac{1}{2}\widehat{xOz}\)
\(\Rightarrow2\widehat{mOz}=\widehat{xOz}\)
CM tương tự, ta được: \(2\widehat{nOz}=\widehat{yOz}\)
Ta có: \(\widehat{xOz}+\widehat{yOz}=180^o\)(2 góc bù nhau)
     \(\Rightarrow2\widehat{mOz}+2\widehat{nOz}=180^o\)
     \(\Rightarrow\widehat{mOz}+\widehat{nOz}=90^o\)
     \(\Rightarrow\widehat{mOn}=90^o\)
     \(\Rightarrow Om\perp On\)
b) Đề của bạn mình thấy nó sai ở chỗ \(Om\perp Az\) vì nhìn hình là thấy không vuông nên mình xin sửa đề thành \(Om\perp At\).
Vì \(Om\perp ON\) (c/m phần a) và At//On:
\(\Rightarrow Om\perp At\) (quan hệ giữa vuông góc và song song)
 

a) \(\Leftrightarrow x^2-x-x^2+2x=5\)
    \(\Leftrightarrow x=5\)
b) \(\Leftrightarrow4x\left(x^2-9\right)=0\)
    \(\Leftrightarrow4x\left(x-3\right)\left(x+3\right)=0 \)
    \(\Leftrightarrow\)\(\left[{}\begin{matrix}4x=0\\x-3=0\\x+3=0\end{matrix}\right.\)
    \(\Leftrightarrow\)\(\left[{}\begin{matrix}x=0\\x=3\\x=-3\end{matrix}\right.\)
Vậy x = 0 , x = 3 hoặc x = -3

\(A=\left(x+y\right)^2-8\left(x+y\right)+2\)
Thay x + y = 5 vào A, ta được:
\(A=5^2-8.5+2=-13\)
Vậy x + y = 5 thì A = -13

1. inactive vaccines
2. live attenuated vaccines
3. people with weaker immune systems
4. antigen
5. subunit vaccine
6. three types of vaccines

1. According to the passage, why is gift-giving important in Vietnam?

A. Because it helps to establish a friendship.                      B. Because it’s common in Vietnamese culture.

C. Because it’s the best way to build up a stable relationship.

D. Because personal relationships play a vital role in Vietnamese culture.

2. Which of the following should not be a reason for gift giving?

A. To show appreciation                                                      B. To bribe somebody

C. To express gratitude                                                        D. To show affection

3. When giving a gift, you should ______________.

A. wrap it in black or white paper                                       B. give it in the business meeting

C. never give sharp objects, such as knives or scissors        D. avoid giving it at a private occasion

4. When receiving a gift, you should ______________.

A. always say “thank you?                                                  B. try to find what is it

C. open it in front of the giver                                             D. ask your host to open it

5. Which of the following is NOT true about gift-giving customs in Vietnam?

A. Gift giving is a good way of strengthening relationships.

B. Gifts for your partners should be given on private occasions.

C. You should avoid giving anything sharp.

D. It is considered rude not to open the gift in front of the giver.

B. Nhật Bản

b) \(=5x\left(3-2x\right)+7\left(3-2x\right)\)
    \(=\left(3-2x\right)\left(5x-7\right)\)
c) \(=\left(x-3\right)^2-y^2\)
    \(=\left(x-3-y\right)\left(x-3+y\right)\)

a) \(=x\left(x^2-4x+4\right)=x\left(x-2\right)^2\)

câu 3 nó loạn hết lên như này 3.smaller / new / old / der / Hoa's / school / scholl / it / than mà vẫn giải được =D, lại còn có thêm chữ one thiếu chữ old. Hiểu vấn đề :-)