Tổng 2 số là : 4

Hiệu hai số là : 2

Số bé là : ( 4 - 2 ) : 2 = 1

Số lớn là : 1 + 2 = 3

Đ/s : 1 và 3

1.We stated learning English four years ago.

=>We have learnt English for 4 years

2.We stated living here fifteen years ago.

➜We have lived here for 15 years

3.Minh began to collect stamps in 2000

➜Minh has collected stamps since 2000

4.It stated to rain at two o'clock

=>It has been raining since 2 o'clock.

5.They began living in this village 2o years ago

=> They have lived in this village for 20 years ago

6.I stated to play the piano ten years ago

=> I have played the piano for ten years

7.They began to live in Ha Noi in 1990

=> They have lived in Ha Noi since 1990

8.They have leanr English for ten years

➜ They stated learning English 10 years ago

9.She has workeras a teacher for 7 years

=> She began working as a teacher 7 years ago

10.She has here for ten yeas .

=> She stated living here 10 years ago

11.They have work in this factery since 2001.

=> They stated working in this factery in 2001

12.He last phoned me in August

=> He hasn't phoned me since August

13.She last wore that dressat her sister's wedding

=> She hasn't wore that dress since her sister's wedding

14.The last time I met Ba wasin 2008

=> I haven't met Ba since 2008

15. The last time she visited me was five months ago

➜She hasn't visited me for 5 months

16.I last wrote to my uncle in July

➜ I haven't written to my uncle since July

17.Minh lats wrote to his pen pal five months ago

➜Minh hasn't written to his pen pal for five months

18. We haven't seen her since we left university

➜ The last time we saw her was when we left university

19.I haven't written to you for a month

➜ I last wrote to you a month ago

20.I last saw Nam two years ago

=> I haven't seen Nam for 2 years

21. The last time she went out with him was 9 months ago

=> It is 9 months since she last went out with him

a) \(f\left(x\right)=6+12=18=0\)(vô lý)

Nên đa thức trên vô nghiệm

\(b,g\left(x\right)=x^2-4=0\\ \Leftrightarrow x^2=4\\ \Leftrightarrow\left[{}\begin{matrix}x=2\\x=-2\end{matrix}\right.\)

Vậy đa thức trên có 2 nghiệm là x=2 ; x= -2

\(c,h\left(x\right)=x^2-16x=0\\ \Leftrightarrow x\left(x-16\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x=16\end{matrix}\right.\)

Vậy...

\(d,t\left(x\right)=x^2+8x=0\\ \Leftrightarrow x\left(x+8\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x=-8\end{matrix}\right.\)

Vậy...

a)Ta có:

\(\left(x-2\right)^2-\left(x-3\right)\left(x-1\right)\\ =x^2-4x+4-x^2+4x-3\\ =1\)

Vậy biểu thức \(\left(x-2\right)^2-\left(x-3\right)\left(x-1\right)\)không phụ thuộc vào biến

b) Ta có:

\(\left(x-1\right)^3-\left(x+1\right)^3+6\left(x+1\right)\left(x-1\right)\\ =x^3-3x^2+3x-1-x^3-3x^2-3x-1+6x^2-6\\ =-8\)

Vậy.....

c) Ta có:

\(\left(x-3\right)\left(x+3\right)\left(x^2+9\right)-\left(x^2-2\right)\left(x^2+2\right)\\ =\left(x^2-9\right)\left(x^2+9\right)-x^4+4\\ =x^4-81-x^4+4=-77\)

Vậy....

d) Ta có: \(\left(3x+1\right)^2-2\left(3x+1\right)\left(3x-5\right)+\left(3x-5\right)^2\\ =\left(3x+1-3x+5\right)^2\\ =6^2=36\)

Vậy....

chiều rộng 12 chiều dài 18 .Mình gặp bài này trong đề cô cho va mình lam đúng