dat \(\frac{2x}{3}=\frac{3y}{4}=k\)--> \(x=\frac{3}{2}k,y=\frac{4}{3}k\)

thay \(x=\frac{3}{2}k,y=\frac{4}{3}k\) vao x²-y²=68 ta duoc

(\(\left(\frac{3}{2}k\right)^2-\left(\frac{4}{3}k\right)^2=68\)

\(\frac{9}{4}k^2-\frac{16}{9}k^2=68\)

\(\frac{17}{36}k^2=68\)

k²=144

k²=12²

k=12 hay k=-12

voi k=12 : x=\(\frac{3}{2}.12=18\) va y=\(\frac{4}{3}.12=16\)

voi k=-12 : x=-18 va y=-16

Complete the following selection ( Hãy hoàn thành bài đọc sau ) : duty, me, proud, love, angle, behaviour, have, take, and, teachers.

YOUR SCHOOL LIFE (cont.)

…. But I look at things from quite a different (1)angle . I’m a student and as such (2) have some duties and responsibilities. I have to do as my parents bid (3)me. to do. I hve to learn something and to read (4) and write a lot. I have to please my teachers by conduct and (5) behavior I have to work hard. If I do my (6)duty diligently I have nothing to be afraid of. I know that my parents at home and the (7) teachers at school are all my wishers. I feel very (8) proud of myshelf when I see that my parents (9)take Care of me. The love of teachers is a rate ting I know all (10) love be very much

1. agree
2. wonderful
3.worried
4.various
5. laughter
6.end
7. heartily
8. transformation
9. flying
10. produced
11. possess
12. indeed
13. students
14. parents

1 + 2 - 3 -  4 + 5 + 6 - 7 - 8 + ...+ 301 + 302

= 1 + (2 -3 - 4 + 5) + (6 - 7 - 8 + 9) + ...+(298 - 299 - 300 + 301) + 302

= 1 + ( 2+5 - 3 - 4) + (6 + 9 - 7 - 8) + ...+(298 + 301 - 299 - 300) + 302

= 1 + (7 - 7) + (15 - 15) + ...+(599 - 599) + 302

= 1+ 0 + 0 + ...+ 0 + 302 = 303 

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