\(\dfrac{-8}{15}=\dfrac{-8\times8}{15\times8}=\dfrac{-64}{150};\dfrac{-5}{-12}=\dfrac{5}{12}=\dfrac{5\times10}{12\times10}=\dfrac{50}{120};\dfrac{3}{8}=\dfrac{3\times15}{8\times15}=\dfrac{45}{120}\)

\(\dfrac{5}{24}=\dfrac{5\times5}{24\times5}=\dfrac{25}{120};\dfrac{11}{40}=\dfrac{11\times3}{40\times3}=\dfrac{33}{120};\dfrac{7}{30}=\dfrac{7\times4}{30\times4}=\dfrac{28}{120}\)

\(\dfrac{-1}{4}=\dfrac{-1\times30}{4\times30}=\dfrac{-30}{120}\)

=>\(\dfrac{50}{120}>\dfrac{45}{120}>\dfrac{33}{120}>\dfrac{28}{120}>\dfrac{25}{120}>\dfrac{-30}{120}>\dfrac{-64}{120}\)

1.not touching

13.dissapointed

14.signed

15.going

nhầm không đọc kĩ đề bài

1.doesn't see

2.brings

3.cries

4.could/was

5.prepares

6.eat

7.sit

8.is

9.forgets

10.play

\(\dfrac{27}{36}=\dfrac{27:9}{36:9}=\dfrac{3}{4};\dfrac{64}{48}=\dfrac{64:16}{48:16}=\dfrac{4}{3};\dfrac{72}{96}=\dfrac{72:24}{96:24}=\dfrac{3}{4}\)

\(\dfrac{54}{78}=\dfrac{54:6}{78:6}=\dfrac{9}{13};\dfrac{65}{95}=\dfrac{65:5}{95:5}=\dfrac{13}{19};\dfrac{25}{100}=\dfrac{25:25}{100:25}=\dfrac{1}{4}\)

\(\dfrac{88}{99}=\dfrac{88:11}{99:11}=\dfrac{8}{9};\)

Câu 7:B

Câu 8:B

II

Câu 1:

a)\(\dfrac{27}{36}=\dfrac{27:9}{36:9}=\dfrac{3}{4}\)

b)\(\dfrac{64}{48}=\dfrac{64:16}{48:16}=\dfrac{4}{3}\)

c)\(\dfrac{72}{96}=\dfrac{72:24}{96:24}=\dfrac{3}{4}\)

d)\(\dfrac{88}{99}=\dfrac{88:11}{99:11}=\dfrac{8}{9}\)

Bài 2:

a)\(\dfrac{11}{12}=\dfrac{11\times4}{12\times4}=\dfrac{44}{48};\dfrac{7}{48}\)

b)\(\dfrac{1}{3}=\dfrac{1\times4}{3\times4}=\dfrac{4}{12};\dfrac{5}{4}=\dfrac{5\times3}{4\times3}=\dfrac{15}{12};\dfrac{10}{12}\)

\(\dfrac{34}{51}=\dfrac{34:17}{51:17}=\dfrac{2}{3}\)

a) Những phân số tối giản là

 \(\dfrac{17}{13}\)

b) Những phân số bằng \(\dfrac{12}{21}\) là

  \(\dfrac{36}{63};\dfrac{48}{84}\)

Gọi bán kính hình thứ thứ hai là R 

=> bán kính hình tròn thứ nhất là 2R

Ta có S\(_1\)=3,14x2Rx2R

          S\(_2\)=3,14xRxR

=>\(\dfrac{S_1}{S_2}=\dfrac{3,14\times2R\times2R}{3,14\times R\times R}=4\)

1