MÌnh làm lun nè : 

1 + 2 + 3 + 4 + 5 + ... + 100 = 5050 

Số số hạng là  : ( 100 - 1 ) : 1 + 1 = 100 

Tổng trên sẽ bằng : ( 1 + 100 ) . 100 : 2 = 5050 

k nah 

if many trees were cut down the air will => would be polluted

Choose the correct answers

1) Choose which has a different stress pattern from the others

A. Festival B. Resource C. Station D. History

2) My sister has been living in Dalat for 2 years; ... , she has never been to Than Tho lake

A. However B. Although C. If D. Because

3) A tradition is something special that is passed down ... the generations

A. With B. Through C. By D. Across

Complete the sentences. Use the Past Simple.

a. I ..stopped.. playing football at 5 p.m. (stop)

b. She ..worked... In a cafe last summer. (work)

c. You .didn't see.. John last week. (not see)

d. did they .go.. to university? (go)

e. Sarah .lived.. in New York in 2002. (live)

f. When .did.. he arrive ? (arrive)

g. Peter .decided.. to travel around Europe. (decide)

h. Luke .had... to dogs and a cat. (have)

Điền từ

tube ; package ; box ; can ; bottle

Use the words in the list to complete these expressions.

she asked me how i (use) to use english in the future

the internet wonderful (invent) invention of the modern life

energy saving bulds should (use ) be used to save electricity\

1 + 2 + 3 + ... + x = 210

số số hạng là : ( x - 1 ) : 1 + 1 = x

tổng : ( x + 1 ) . x : 2 = 210

        ( x + 1 ) . x = 420

     Mà 21 x 20 = 420

=> x = 20

102 nha ban

\(\frac{\left(x^6+3x^4\sqrt{x^2-x+1}\right)\left(3+x-x^2\right)}{4\left(2+\sqrt{x^2-x+1}\right)\left(x^2-x+1\right)}=\sqrt{x^2-x+1}\left(2-\sqrt{x^2-x+1}\right)\)

\(pt\Leftrightarrow\left(x^6+3x^4\sqrt{x^2-x+1}\right)\left(3+x-x^2\right)=4\left(2+\sqrt{x^2-x+1}\right)\left(x^2-x+1\right)\sqrt{x^2-x+1}\left(2-\sqrt{x^2-x+1}\right)\)

\(\Leftrightarrow\left(3+x-x^2\right)\left(x^6+3x^4\sqrt{x^2-x+1}\right)=\left(3+x-x^2\right).4\left(x^2-x+1\right)\sqrt{x^2-x+1}\)

\(\Leftrightarrow\orbr{\begin{cases}3+x-x^2=0\left(1\right)\\x^6+3x^4\sqrt{x^2-x+1}=4\left(x^2-x+1\right)\sqrt{x^2-x+1}\left(2\right)\end{cases}}\)

\(\left(1\right)\Leftrightarrow x=\frac{1+or-\sqrt{13}}{2}\)

\(\left(2\right)\Leftrightarrow x^6+3x^4\sqrt{x^2-x+1}-4\left(x^2-x+1\right)\sqrt{x^2-x+1}=0\)

Đặt: \(a=x^2;b=\sqrt{x^2-x+1}\)

\(pt\Leftrightarrow a^3+3a^2b-4b^3=0\Leftrightarrow\left(a-b\right)\left(a+2b\right)^2=0\)

\(\Leftrightarrow x^2=\sqrt{x^2-x+1}\Leftrightarrow\left(x-1\right)\left(x^3+x^2+1\right)=0\) 

..... Bình phương lên giống cô Huyền nói :D

co 2 so

1. What's/ your/ the/ with/matter/ mother/?

=> what's the matter with your mother?

2. had/ Quan/ to/ the/ headache/ doctor/ because/ went/ he/ a/.

=> quan went to the doctor because he had a headache

3. school/ Mai/ bad/ come/ to/ can't/ because/ she/ cold/ has/ a/.

=> Mai can't come to school because she has a bad cold

4. well/ I/ feel/ don't/.

=> i don't feel well

5. I'm/ health/ sorry/ to/ about/ hear/ very/ your/.

=> i'm very sorry to hear sbout your health