4.

hai số đó là:9 và 25

5.

84=2².3.7

Ư(84)={1;2;3;4;6;7;12;14;21;42;28;84} nha

 mong được tic

a, \(\left\{{}\begin{matrix}35x-28y=21\\35x-45y=40\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}17y=-19\\x=\dfrac{3+4y}{5}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=-\dfrac{19}{17}\\x=-\dfrac{13}{17}\end{matrix}\right.\)

b, Đặt x;y khác 0 

Đặt 1/x = t ; 1/y = u 

\(\left\{{}\begin{matrix}t-8u=18\\5t+4u=51\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}5t-40u=90\\5t+4u=51\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}-44u=39\\t=18+8u\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}u=-\dfrac{39}{44}\\t=\dfrac{120}{11}\end{matrix}\right.\)

Theo cách đặt y = -44/39 ; x = 11/120 (tm)

\(a,\\ \Leftrightarrow\left\{{}\begin{matrix}35x-28y=21_{\left(1\right)}\\35x-45y=40_{\left(2\right)}\end{matrix}\right.\\ Lấy\left(1\right)-\left(2\right),ta.đc:\\ -17y=19\Leftrightarrow y=\dfrac{-19}{17}\\ Thay.vào.\left(1\right):\\ 35x-28.\dfrac{-19}{17}=21\Leftrightarrow x=\dfrac{-5}{17}\) 

Vậy ......

\(b,\\ \Leftrightarrow\left\{{}\begin{matrix}\dfrac{1}{x}=18+\dfrac{1}{y}\\5.\left(18+\dfrac{1}{y}\right)+\dfrac{4}{y}=51\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}\dfrac{1}{x}=18+\dfrac{1}{y}\\\dfrac{9}{y}=-39\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\dfrac{1}{x}=18-\dfrac{13}{3}\\\dfrac{1}{y}=\dfrac{-13}{3}\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}\dfrac{1}{x}=\dfrac{41}{3}\\\dfrac{1}{y}=\dfrac{-13}{3}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{3}{41}\\y=\dfrac{-3}{13}\end{matrix}\right.\)

1. go      2. read       3. study      4. watch     5. see

6. talk    7. move      8. look        9. drink      10. eat

11. bring    12. walk    13. sleep    14. do      15. give

16. cook     17. visit      18. take     19. sit   20. stand

Chúc bạn học tốt☺

1 do

2 eat

3 cook

4 go

5 write

6 see

7 walk

8 climb

9 move

10 sleep

11 run

12 play 

13 wash

14 drive

15 talk 

16 sit

17 plant

18 bring

19 drink

20 buy

Có gì sai thì chỉ mình với :>

1. lie: nói dối

2. wash: rửa

3. cry: khóc

4. brush: chải

5. arrive: đến

6. ask: hỏi

7. watch: xem 

8. play: chơi

9. liisten: nghe

10. cook: nấu

11. visit: thăm

12. grow: lớn lên

13. refer: giới thiệu

14. hug: ôm

15. look: nhìn

16. leave: rời khỏi

17. live: sống, trực tiếp

18. investigate: điều tra

19. return: trở về

20. walk: đi bộ    

=>29x+696=928

=>29x=232

hay x=8

x=8 ^-^

=>29x+696=928

=>29x=232