Ta có : x^2 + y^2 +1 >= xy +x +y

   <=> 2(x^2+y^2 +1) >=2 ( xy+x+y)     (*nhân 2 vào cả 2 vế)

    <=> 2x^2+2y^2+2 >= 2xy+2x+2y

   <=> 2x^2+2y^2+2-2xy-2x-2y >= 0

    <=> x^2-2xy+y^2+x^2-2x+1+y^2-2y+1 >=0

<=> (x-y)^2 + ( x-1)^2 +(y-1)^2 >= 0

+ Với x,y thì  (x-y)^2 >= 0;(x-1)^2>=0;(y-1)^2>=0 nên ...(ghi lại dòng trên) 

Vậy : x^2 +y^2+1 >= xy+x+y

1. the/ borrow/ books/ students/ can/ from/ library.

Students can borrow book from the library.

2. many/ put/ of/ are/ kinds/ shelves/ books/ the/ on.

many kinds of books  are on the shelves

3. and/ subjects/ Math/ English/ are/ subjects/ favorite.

math and EL are my favorite subjects.

4. usually/ Wednesday/ Friday/ and/ have/ we/ on/ Literature.

we usually have literature on wednesday and friday.

5. school/ time/ what/ open/ time/ our/ does?

what time does our school open?

6. Math/ Chemistry/ English/ have/ and/ today/ I.

i have math, chemistry and EL today.

7. tomorrow/ will/ go/ school/ we/ not/ go.

we will not go to school tomorrow.

8. Literature/ will/ forty/ our/ eight/ class/ start/ at.

our literature class will start forty eight.

1:Tia Oz nằm giữa tia Ox và Oy sao cho góc xOz=zOy

2:xOz=zOy=\(\frac{xOy}{2}\)

1.What would you like?

2.How often do you write to your pen?

3.How far is it from hanoi to ho chi minh city?

4.What does your penpal tell you?

9 giờ 12 phút

96 km

1.or

2.does trung have

3.an

1. It's three kilometers from my house to the supermarket.

how far is it from your house to the supermarket?

2. The Amazon River is 6,750 kilometers long.

how long is the amazon river?

3. Mount Everest is 8,863 meters high.

how high is mount everest?

4. Tam is 1,48 meters tall.

how tall is tam?

5. My classroom is large. It measures 5 by 7 meters.

how large is your classroom?

6. Hoa is thirteen years old.

how old is hoa?

7. Tam goes to the school library three times a week.

how often does she go to to school?

8. Huong speaks English very well.

how does huong speak english?

9. Ha Noi is very cold in winter.

how is hanoi in winter?

10. There are 42 students in Hoa's class.

how many students are there in hoa's class?

1. She studies Math on Monday and Thursday.

When does she study maths?

2. Our most popular after-school activity is badminton.

what is your most popular after-school activity?

3. The library opens at 7.30 in the morning.

what time does the library open?

4. The school library contains over 20 thousand books.

how many books does the library contains?

5. Over 5000 people work in the United States' Library of Congress.

how many people work in the united status's library of congress?

6. I often go to play football with my friends in the afternoon.

who do you often go to play football with in the afternoon?

7. My mother is cooking in the kitchen

what is your mother doing in the kitchen?

My brother ( not live ) .........doesn't live....................in Manchester . He (live) ...........lives................in LONDON
Our school ( have) ...........have..................a small garden . There ( be) ..........are...............many flowers in it .
what time does your mother ( get up ) ........get up.......................every morning ?
 Nam 's brother (watch )............watches........................TV everyningt 
Hoa (wash)............washes..........her face at six o'clock .
We (not have) ...............don't have...............breakfast at seven this every morning
I (be)...........am.................a nurse but my parents ( not be ) ......aren't..............nurses 
Your parents (go).........go...................to work at eight