\(\frac{a}{27}=\frac{-5}{9}=\frac{-45}{b}\)

\(=>\frac{a.3}{81}=\frac{-45}{81}=\frac{-45}{b}\)

=>b=81

     a.3=-45

     a=-15

Vậy a=-15;b=81

b: \(x+\dfrac{5}{6}=\dfrac{3}{8}\)

=>\(x=\dfrac{3}{8}-\dfrac{5}{6}\)

=>\(x=\dfrac{9}{24}-\dfrac{20}{24}=-\dfrac{11}{24}\)

c: \(\dfrac{2}{3}x-\dfrac{1}{2}=\dfrac{5}{6}\)

=>\(\dfrac{2}{3}x=\dfrac{5}{6}+\dfrac{1}{2}=\dfrac{8}{6}=\dfrac{4}{3}\)

=>2x=4

=>x=4/2=2

d: \(\dfrac{x}{7}=\dfrac{6}{-21}\)

=>\(\dfrac{x}{7}=\dfrac{-2}{7}\)

=>x=-2

e: \(\left(\dfrac{7}{3}x-0,6\right):\dfrac{3^2}{5}=1\)

=>\(\dfrac{7}{3}x-0,6=\dfrac{3^2}{5}=1,8\)

=>\(\dfrac{7}{3}x=2,4\)

=>\(x=2,4:\dfrac{7}{3}=2.4\cdot\dfrac{3}{7}=\dfrac{7.2}{7}=\dfrac{36}{35}\)

f: \(\dfrac{x}{45}=\dfrac{5}{6}+\dfrac{-29}{30}\)

=>\(\dfrac{x}{45}=\dfrac{25}{30}-\dfrac{29}{30}=-\dfrac{4}{30}=-\dfrac{2}{15}\)

=>\(x=-\dfrac{2}{15}\cdot45=-6\)

g: \(\left(4,5-2x\right)\cdot\left(-\dfrac{1^4}{7}\right)=\dfrac{11}{14}\)

=>\(4,5-2x=\dfrac{11}{14}:\dfrac{-1}{7}=\dfrac{-11}{2}\)

=>\(2x=4,5+\dfrac{11}{2}=\dfrac{20}{2}=10\)

=>x=10/2=5

h: \(-\dfrac{2}{7}+\dfrac{4}{7}x=\dfrac{5}{7}\)

=>\(\dfrac{4}{7}x=\dfrac{5}{7}+\dfrac{2}{7}=\dfrac{7}{7}\)

=>4x=7

=>\(x=\dfrac{7}{4}\)

MÌNH ĐANG CẦN GẤP

a, 2x+ 1/4 = 3/2

2x = 3/2-1/4

2x = 5/4

x=5/4:2

x= 5/8 

b, (x-5) - 1/3 = 2/5

x-5= 2/5+1/3

x-5=11/15

x=11/15+5

x=86/15

c, (4,5-2x):3/4=4/3

(4,5-2x)=4/3. 3/4

4,5-2x=1

2x= 5,5

x=5,5:2

x=2,75

a) 2x+1/4=3/2

=> 2x      =3/2-1/4

=> 2x       =5/4

=> x         =5/4:2

=> x         =5/8

b) (x-5)-1/3=2/5

=>  x-5      =2/5+1/3

=> x-5        =11/15

=> x           =11/15+5

=> x           =86/15

c) (4,5-2x):3/4=4/3

=> 4,5-2x       =4/3x3/4

=> 4,5-2x       =1

=>   2x          =4,5-1

=>   2x           =3,5

=>    x             =3,5:2

=>    x             =1,75

a) \(3\frac{1}{3}\left(3\frac{1}{4}+2x\right)=6\frac{2}{3}\)

   \(3\frac{1}{3}\times3\frac{1}{4}+2x=6\frac{2}{3}\)

   \(10\frac{5}{6}+2x=6\frac{2}{3}\)

   \(2\times x=6\frac{2}{3}+10\frac{5}{6}=17,5\)

   \(x=17,5\div2=8,75\)

Vậy x = 8,75

b) \(x-25\%x=\frac{6}{11}\left(\frac{1}{2}+\frac{3}{4}-\frac{1}{3}\right)\)

   \(x-\frac{25}{100}x=\frac{6}{11}\left(\frac{1}{2}+\frac{3}{4}-\frac{1}{3}\right)\)

   \(x-\frac{1}{4}\times x=\frac{6}{11}\times1\frac{7}{12}=\frac{19}{22}\)

   \(x\times x=\frac{19}{22}+\frac{1}{4}=\frac{49}{44}\)

\(\Rightarrow2x\left(x\times x\right)=\frac{49}{44}\)   

   \(x=\frac{49}{44}\div2=\frac{49}{88}\)

   Vậy x = \(\frac{49}{88}\)

c) \(\left(4,5-2x\right)\times1\frac{4}{7}=\frac{11}{14}\)

   \(4,5-2x\times1\frac{4}{7}=\frac{11}{14}\)

   \(-2x\times1\frac{4}{7}=\frac{11}{14}-4,5=-3\frac{5}{7}\)

   \(-2\times x=-3\frac{5}{7}\div1\frac{4}{7}=-2\frac{4}{11}\)

   \(x=-2\frac{4}{11}\div\left(-2\right)=1\frac{2}{11}\)

Vậy x = \(1\frac{2}{11}\)

d) \(-3^2-|2x+3|=4\)

    \(9-|2x+3|=4\)

   \(-|2x+3|=4-9=-5\)

   \(-|2x|=-5-|3|=-8\)

   \(-|x|=-8\div2=-4\)

    \(-x=4\Rightarrow x=-4\)

   Vậy x = -4 (-x được xem là số đối của x)