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My school is ....( điền tên trường bn ) ........This Saturday, our History teachers will celebrate a History competiton. Each class votes 1 student to take part in this competition. And the law is that: The teachers will give each representative of each class a number of time, then he/she must guest the event of this time, the more you guest, the more points you get. with each event, the group will get 5 points. And the winner is the representative who get the most marks. The winner will be awarded a CD of History f Vietnam. This competition is donated by the Student's Parents society.
Bài làm:
Ta có: \(\frac{a}{b}=\frac{b}{c}\) => \(b^2=ac\)
Thay vào ta được: \(\frac{a^2+b^2}{b^2+c^2}=\frac{a^2+ac}{ac+c^2}=\frac{a\left(a+c\right)}{c\left(a+c\right)}=\frac{a}{c}\)
Vậy \(\frac{a}{c}=\frac{a^2+b^2}{b^2+c^2}\)
Đặt \(\frac{a}{b}=\frac{b}{c}=k\Rightarrow\hept{\begin{cases}a=kb\\b=kc\end{cases}}\Rightarrow a=k^2c\)
\(\frac{a^2+b^2}{b^2+c^2}=\frac{\left(k^2c\right)^2+\left(kc\right)^2}{\left(kb\right)^2+c^2}=\frac{k^4b^c+k^2c^2}{k^2b^2+c^2}=\frac{k^2\left(k^2b^2+c^2\right)}{k^2b^2+c^2}=k^2=\frac{a}{c}\)( đpcm )
1. A. children B. teacher C. chair D. school
2. A. sport B. hot C. rod D. pot
3. A. daughter B. sauce C. aunt D. laundry
4. A. morning B. forget C. pork D. forty
5. A. pleasure B. leisure C. closure D. sure
6. A. burn B. sun C. hurt D. turn
7. A. although B. enough C. cough D. photo
8. A. discussion B. vision C. treasure D. decision
9. A. candy B. cook C. cycling D. clever
10. A. jeans B. orange C. growth D. generous
1. a 'havest b 'famous c de'sign
2. a 'monday b o'ccasion c 'flower
3. a e'vent b 'special c 'tourist
ĐA :1C
2B
3A
Hoa (write) _____write____ to her pen pal in the USA every month.
When being a child, she received a good (educate) _____education______ .
đề
11. A. time
B. kind
C. bid
D. nice
12. A. hard
B. carry
C. card
D. yard
13. A. my
B. baby
C. spy
D. cry
14. A. well
B. get
C. send
D. pretty
15. A. weather
B. ready
C. mean
D. head
16. A. break
B. mean
C. please
D. meat
17. A. lucky
B. punish
C. pull
D. hungry
18. A. planet
B. character
C. happy
D. classmate
19. A. letter
B. twelve
C. person
D. sentence
20. A. humor
B. music
C. cucumber
D. sun