\(a.\)

\(\dfrac{-28}{35}=\dfrac{16}{x}\)

\(\Rightarrow x=\dfrac{35\cdot16}{-28}=\dfrac{5\cdot7\cdot4\cdot4}{-7\cdot4}=-20\)

\(b.\)

\(\dfrac{x+7}{15}=\dfrac{-24}{36}\)

\(\Rightarrow x+7=\dfrac{15\cdot-24}{36}=\dfrac{5\cdot3\cdot-12\cdot2}{12\cdot3}=-10\)

\(\Leftrightarrow x=-17\)

Bài 2:

a: -2*(-27)=54

6*9=54

=>Hai phân số này bằng nhau

b: -1/-5=1/5=5/25<>4/25

Bài 3:

a: =>16/x=-4/5

=>x=-20

b: =>(x+7)/15=-2/3

=>x+7=-10

=>x=-17

a) \(\dfrac{-2}{9}\) và \(\dfrac{6}{-27}\)

\(\dfrac{6}{-27}=\dfrac{6:\left(-3\right)}{\left(-27\right):\left(-3\right)}=\dfrac{-2}{9}\)

Vậy \(\dfrac{-2}{9}=\dfrac{6}{-27}\)

b) \(\dfrac{-1}{-5}\) và \(\dfrac{4}{25}\)

\(\dfrac{-1}{-5}=\dfrac{\left(-1\right).\left(-5\right)}{\left(-5\right).\left(-5\right)}=\dfrac{5}{25}\)

Do \(5\ne4\Rightarrow\dfrac{5}{25}\ne\dfrac{4}{25}\)

Vậy \(\dfrac{-1}{-5}\ne\dfrac{4}{25}\)

Bài 3

a) \(\dfrac{-28}{35}=\dfrac{16}{x}\)

\(x=\dfrac{35.16}{-28}\)

\(x=-20\)

b) \(\dfrac{x+7}{15}=\dfrac{-24}{36}\)

\(\left(x+7\right).36=15.\left(-24\right)\)

\(36x+252=-360\)

\(36x=-360-252\)

\(36x=-612\)

\(x=\dfrac{-612}{36}\)

\(x=-17\)

a: \(A=\dfrac{-7}{28}\cdot\dfrac{15}{25}=\dfrac{-1}{4}\cdot\dfrac{3}{5}=\dfrac{-3}{20}\)

b: \(B=\dfrac{-5\cdot7}{14\cdot\left(-3\right)}=\dfrac{35}{42}=\dfrac{5}{6}\)

c: \(C=\dfrac{-1}{5}-\dfrac{1}{5}\cdot\dfrac{3}{5}=\dfrac{-1}{5}-\dfrac{3}{25}=\dfrac{-8}{25}\)

d: \(D=\dfrac{-3}{4}-\dfrac{1}{4}=-1\)

e: \(E=\dfrac{-4}{5}\left(1-\dfrac{15}{16}\right)=\dfrac{-4}{5}\cdot\dfrac{1}{16}=\dfrac{-1}{20}\)

f: \(F=\dfrac{6-7}{4}\cdot\dfrac{4+12}{22}=\dfrac{-1}{4}\cdot\dfrac{8}{11}=\dfrac{-2}{11}\)

\(x=\dfrac{35.16}{-28}\)

\(x=-20\)

\(\dfrac{-28}{35}=\dfrac{16}{x}\\ \Rightarrow-28\cdot x=35\cdot16=560\\ x=560:-28\\ x=-20\)

\(x=\dfrac{35.16}{-28}=20\)

11/9-5/6:15

=11/9-5/6.1/15

=11/9-1/18

=7/6

3/16+(-7/30).15/28

=3/16+(-1/8)

=3/16+(-2/16)

=1/16

\(\dfrac{11}{9}-\dfrac{5}{6}:15=\dfrac{11}{9}-\dfrac{5}{6}\times\dfrac{1}{15}=\dfrac{11}{9}-\dfrac{5}{90}=\dfrac{110}{90}-\dfrac{5}{90}=\dfrac{105}{90}=\dfrac{7}{6}\)

\(\dfrac{3}{16}+\dfrac{-7}{30}\times\dfrac{15}{28}=\dfrac{3}{16}+\left(-\dfrac{1}{8}\right)=\dfrac{3}{16}-\dfrac{1}{8}=\dfrac{3}{16}-\dfrac{2}{16}=\dfrac{1}{16}\)

\(\dfrac{7}{21}+\dfrac{-9}{36}=\dfrac{1}{3}+\dfrac{-1}{4}=\dfrac{4}{12}+\dfrac{-3}{12}=\dfrac{1}{12}\)

\(\dfrac{-12}{18}+\dfrac{-21}{35}=\dfrac{-2}{3}+\dfrac{-3}{5}=\dfrac{-10}{15}+\dfrac{-9}{15}=\dfrac{-19}{15}\)

\(\dfrac{-18}{14}+\dfrac{15}{-21}=\dfrac{-9}{7}+\dfrac{-5}{7}=\dfrac{-14}{7}=-2\)

\(\dfrac{3}{21}+\dfrac{-6}{42}=\dfrac{1}{7}+\dfrac{-1}{7}=0\)

a: =>1/x=4

hay x=1/4

b: =>x+7=-10

=>x=-17

c: =>x²=36

=>x=6 hoặc x=-6

d: =>(x-3)²=16

=>x-3=4 hoặc x-3=-4

=>x=7 hoặc x=-1

\(a,\dfrac{1}{-x}=-4\\ \Rightarrow\left(-x\right)\left(-4\right)=1\\ \Rightarrow4x=1\\ \Rightarrow x=\dfrac{1}{4}\\ b,\dfrac{x+7}{15}=\dfrac{-24}{36}\\ \Rightarrow\dfrac{x+7}{15}=\dfrac{-2}{3}\\ \Rightarrow3\left(x+7\right)=-2.15\\ \Rightarrow3x+21=-30\\ \Rightarrow3x=-51\\ \Rightarrow x=-17\)

\(c,\dfrac{x}{-3}=\dfrac{-12}{x}\\ \Rightarrow x.x=\left(-3\right)\left(-12\right)\\ \Rightarrow x^2=36\\ \Rightarrow x=\pm6\)

\(d,\dfrac{-2}{x-3}=\dfrac{x-3}{-8}\\ \Rightarrow\left(x-3\right)\left(x-3\right)=\left(-2\right)\left(-8\right)\\ \Rightarrow\left(x-3\right)^2=16\\ \Rightarrow\left[{}\begin{matrix}x-3=4\\x-3=-4\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=7\\x=-1\end{matrix}\right.\)

a.\(\Leftrightarrow4x=1\Leftrightarrow x=\dfrac{1}{4}\)

b.\(\Leftrightarrow\left(x+7\right).36=-360\Leftrightarrow x+7=-10\Rightarrow x=-17\)

c.\(x^2=36\Leftrightarrow x=6;-6\)

d.\(-2.-8=\left(x-3\right)\left(x-3\right)\Leftrightarrow16=x^2-6x+9\Leftrightarrow x^2-6x-7=0\Rightarrow x=7;-1\)

a)\(x=\left(\dfrac{3}{56}\cdot\dfrac{28}{9}\right):\dfrac{-3}{7}=\dfrac{1}{6}:\dfrac{-3}{7}=-\dfrac{7}{18}\)

b)\(x=\left(\dfrac{7}{15}\cdot\dfrac{5}{3}\right)+\dfrac{3}{16}=\dfrac{7}{9}+\dfrac{3}{16}=\dfrac{139}{144}\)

c)\(x=\left(\dfrac{5}{6}-\dfrac{2}{5}\right).5=\dfrac{13}{6}\)

d)\(=>x\left(\dfrac{3}{4}-\dfrac{2}{5}\right)=\dfrac{1}{6}\cdot\left(\dfrac{3}{7}+\dfrac{5}{7}\right)\)

\(x\cdot\dfrac{7}{20}=\dfrac{4}{21}=>x=\dfrac{4}{21}\cdot\dfrac{20}{7}=\dfrac{80}{147}\)