a)"\(\forall x\in R|x^4-x^2-2x+3>0\)''

b)\(x^4-x^2-2x+3\)

=\((x^4-2x^2+1)+(x^2-2x+1)+1\)

=\((x^2-1)^2+\left(x-1\right)^2+1>1\) (luôn đúng)

Vậy\(x^4-x^2-2x+3>0\) (đpcm)

{[(32 + 1 ) . 10 - ( 8:2 + 6 )]: 2} + 55 - (10 : 5)3

=\(\left\{\left[33.10-(4+6)\right]:2\right\}+55-2.3\)

=\(\left\{\left[330-10\right]:2\right\}+55-6\)

=\(\left\{320:2\right\}+49\)

=\(160+49\)

=209

1.Hạt nhân

2.proton

3.notron

4.electron

5. proton

6.electron

7. trung hòa về điện

Gọi Hợp chất cần tìm là A₂O₃

\(\Rightarrow\)x là nguyên tử khối của nguyên tố A

Theo bài ra :

\(\dfrac{m_O}{m_{A_2O_3}}\)=\(\dfrac{16\times3}{x\times2+16\times3}\)=\(\dfrac{30}{100}\)=\(\dfrac{3}{10}\)

\(\Rightarrow\)x =56

\(\Rightarrow\) Nguyên tố A là Sắt (III) .Fe

Gọi: l 0  là chiều dài ở  0 ° C ; l là chiều dài ở  t ° C ;  α  là hệ số nở dài. Công thức tính chiều dài l  ở  t ° C  là:

A.  l = l 0 ( 1 + α t ) .

B.  l = l 0 α t .

C.  l = l 0 + α t .

D.  l = l 0 1 + α t

Choose the word or phrase among A, B, Cor D that best fits the blank space in the following passage.

Role of Teachers

The changes that (1)……. in schools have changed the roles of teachers. In the past, teachers used to be the (2) ……..source of knowledge, the leader and educator of their students' school life. Nowadays, teachers provide information and show their students how to (3)…….. it. Although they are still considered to be a kind of (4)……….. in the class, they can be thought of as facilitators in the learning (5)………..

Another difference between the past and present tasks of teachers is represented by the technical (6)……… they need to be able to use and handle effectively, such as computer, photocopier, PowerPoint, projectors, etc. Instead of teaching (7)……… chalk, they need tobe an information technology expert.

One of the biggest challenges for teachers is that their role in the school management has also changed. The school needs them as individuals, who can make decisions and cope with the stress of the (8)……….. world of schools. At the same time teachers need to be able to work in teams, and (9)……….. with colleagues and parents. A teacher has not only to instruct but also to (10)…….. the students with confidence and determination.

Question 1

A.existed

B.took place

C.occurring

D.took first place

1 spending -playing

2making

3. not to make

4 turning

5.giving

6. building

7. advising

8. buying

9. watching - to give

10. come