x/30 + 4/5= 79/30

x/30 = 79/30 - 4/5

x/30= 11/6

11/6= 55/30

=> x= 55

\(x-\dfrac{4}{12}=-\dfrac{5}{6}\)

⇔\(x-\dfrac{1}{3}=-\dfrac{5}{6}\)

⇔\(x=-\dfrac{1}{2}\)

\(\Leftrightarrow x=-\dfrac{1}{2}\)

=>(x-4).6=12.(-5)

=>6x-24=-60

=>6x=-36

=x=-6

Bài 1: 

\(=\dfrac{-3-39}{42}+\dfrac{-6-11}{17}-\dfrac{1}{6}=-\dfrac{119}{48}\)

Bài 2: 

=>x:5=-13/20

hay x=-65/20=-13/4

Bài 1: 

\(=\dfrac{-3-39}{32}+\dfrac{-6-11}{17}+\dfrac{-1}{6}=-\dfrac{21}{16}+\dfrac{-1}{6}-1=-\dfrac{119}{48}\)

Bài 2: 

\(\Leftrightarrow x:5=-\dfrac{13}{20}\)

hay x=-13/4

⇔x:5=−1320⇔x:5=−1320

hay x=-13/4

\(x\times\dfrac{4}{5}=3-\dfrac{2}{5}\)

\(x\times\dfrac{4}{5}=\dfrac{13}{5}\)

\(x=\dfrac{13}{5}:\dfrac{4}{5}\)

\(x=\dfrac{13}{5}\times\dfrac{5}{4}\)

\(x=\dfrac{13}{4}\)

Chiều dài HCN là :

  \(\dfrac{5}{6}:\dfrac{2}{3}=\dfrac{5}{4}\left(m\right)\)

Chu vi HCN là :

  \(\left(\dfrac{5}{4}+\dfrac{2}{3}\right)\times2=\dfrac{23}{6}\left(m\right)\)

     Đ/s :...

\(x\times\dfrac{4}{5}=\dfrac{13}{5}\\ x=\dfrac{13}{5}\div\dfrac{4}{5}\\ x=\dfrac{13}{4}\)

\(CD=\dfrac{5}{6}\div\dfrac{2}{3}=\dfrac{5}{4}\\ P=\left(\dfrac{5}{4}+\dfrac{2}{3}\right)\times2=\dfrac{23}{6}\)

\(=\left(x^3+x^2\right)-\left(7x^2+7x\right)+\left(19x+19\right)=\left(x+1\right)\left(x^2-7x+19\right)=0\)

Ta thấy:  \(x^2-7x+19=x^2-2\times\frac{7}{2}x+\frac{7}{2}^2+\frac{27}{4}=\left(x-\frac{7}{2}\right)^2+\frac{27}{4}\ge\frac{27}{4}\)lớn hơn 0

\(\Rightarrow x+1=0\Rightarrow x=-1\)

\(x^3-6x^2+12x+19=0\)

\(\Leftrightarrow\left(x^3+x^2\right)-\left(7x^2+7x\right)+\left(19x+19\right)=0\)

\(\Leftrightarrow\left(x+1\right)\left(x^2-7x+19\right)=0\)

Mà \(x^2-7x+19>0\)với \(\forall x\)

\(\Rightarrow x+1=0\)

\(\Leftrightarrow x=-1\)

Vậy \(x=-1\)

\(\frac{5}{6}+\frac{\left(-19\right)}{30}=\frac{x}{5}\)

\(\frac{25}{30}+\frac{\left(-19\right)}{30}=\frac{x}{5}\)

\(\frac{6}{30}=\frac{x}{5}\)

\(\frac{1}{5}=\frac{x}{5}\)

\(\Rightarrow5x=5\times1\)

\(5x=5\)

\(x=5\div5\)

\(x=1\)

\(\frac{5}{6}+\frac{-19}{30}=\frac{x}{5}\)

\(\Leftrightarrow\frac{x}{5}=\frac{5}{6}+\frac{-19}{30}\)

\(\Leftrightarrow\frac{x}{5}=\frac{25}{30}+\frac{-19}{30}\)

\(\Leftrightarrow\frac{x}{5}=\frac{6}{30}\)

\(\Leftrightarrow\frac{x}{5}=\frac{1}{5}\)

\(\Rightarrow x=1\)

Vậy \(x=1\)

Ta có: x(1+30%)=-1,31

  ⇒        \(\dfrac{13}{10}\)x         =-1,31

  ⇒         x             =-1,31 : \(\dfrac{13}{10}\)

  ⇒         x             = -\(\dfrac{131}{130}\)

x + 30% x = -1,31

\(x+\dfrac{30}{100}x=-1,31\)

x+0,3x=-1,31

x.(0,3+1)=-1,31

x.1,3=-1,31

\(x=\dfrac{-1,31}{1,3}\)

\(x=-\dfrac{131}{130}\)

x = 4/5 : 3/4

x = 16/15

x = 5/9 : 8/3

x = 5/9 x 3/8

x = 5/24

\(x=\dfrac{4}{5}\times\dfrac{4}{3}\)

\(x=\dfrac{16}{15}\)

-----------------------

\(x=\dfrac{5}{9}\times\dfrac{3}{8}\)

\(x=\dfrac{5}{24}\)

\(x\times\dfrac{3}{4}=\dfrac{4}{5}\)

\(x=\dfrac{4}{5}:\dfrac{3}{4}\)

\(x=\dfrac{4}{5}\times\dfrac{4}{3}\)

\(x=\dfrac{16}{15}\)

\(\dfrac{5}{9}:x=\dfrac{8}{3}\)

      \(x=\dfrac{5}{9}:\dfrac{8}{3}\)

      \(x=\dfrac{5}{9}\times\dfrac{3}{8}\)

     \(x=\dfrac{15}{72}\)

    \(x=\dfrac{5}{24}\)