Gọi chiều dài và chiều rộng của hình chữ nhật là a và b

    Diện tích là a.b=49cm²

Chúng tỉ lệ với 3 và 4 

Suy ra \(\frac{a}{3}=\frac{b}{4}\)

    Áp dụng dãy tỉ số bằng nhau ta có 

\(\frac{a}{3}=\frac{b}{4}\)=\(\frac{a.b}{3.4}=\frac{49}{7}=7\)

Do đó:

\(\frac{a}{3}=7\) a=7x3=21

\(\frac{b}{4}=7\) b=7x4=28

     Vậy a=21

            b=28

1: Her sad story made me city

....................It was her sad stories that made me cry.........................

2: You are to blame for the damage

......................... It is you who are to blame for the damage/ It is you that is to blame for the damage..........................

3: We reallly enjoy hiking in the ferest

.......................It's hiking in the forest that we really enjoy......................................

4: You should really speak to your parent when you have problems

.................... It's your parents that / who you should really speak to when you have problems.........................

5: I dislike his dishonesty the most

..............It's his dishonesty that I dislike the most.....................

6: Lana is a relationship with Jim

...............It's Jim that / who Lana is in a relationship with...................

7: He became successful as a famous writer at the age of 20

.......It was at the age of 20 that he became successful as a famous writer..............

8: they had their first date in a nice coffee shop

..................... It was in a nice coffee shop that they had their first date...............................

sai đề rồi bạn ơi sao lại make me city ?

theo sách thì là make me cry nha bạn