a,3/4 . (-5/12)+3/4.(-7/12)

` 3/4 . [ - ( 5/12 + 7/12  ) ] `

`3/4 . (-1) = -3/4 `

`2/3 . x - 0,5 = 3/4 `

`        x - 0,5 = 3/4 - 2/3 `

`        x-0,5 = 1/12 `

`        x =       1/12 + 0,5 `

`        x= 7/12 `

a, 3/4 . (-5/12)+3/4.(-7/12) 

= 3/4 . [(-5/12) + (-7/12)]

= 3/4 . (-1)

= -3/4

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

a, 2/3 .x-0,5=3/4

2/3 . x = 3/2 + 0,5

2/3 . x = 2 

x = 2 : 2/3

x = 3 

vậy x = 3

Bài 2:

a: =>2/3x=3/4+1/2=3/4+2/4=5/4

=>x=5/4:2/3=5/4*3/2=15/8

b:=>-2x+4=3x-12

=>-5x=-16

=>x=16/5

\(a.x+\dfrac{1}{6}=-\dfrac{3}{8}\)

\(\Leftrightarrow x=-\dfrac{13}{24}\)

\(b.2-\left(\dfrac{3}{4}-x\right)=\dfrac{7}{12}\)

\(\Leftrightarrow2-\dfrac{3}{4}+x=\dfrac{7}{12}\)

\(\Leftrightarrow x=-\dfrac{2}{3}\)

\(c.\dfrac{1}{2}x+\dfrac{1}{8}x=\dfrac{3}{4}\)

\(\Leftrightarrow\dfrac{5}{8}x=\dfrac{3}{4}\)

\(\Leftrightarrow x=\dfrac{6}{5}\)

\(d.75\%-1\dfrac{1}{2}+0,5:\dfrac{5}{12}-\left(\dfrac{-1}{2}\right)^2\)

\(=\dfrac{75}{100}-\dfrac{3}{2}+\dfrac{1}{2}:\dfrac{5}{12}-\dfrac{1}{4}\)

\(=-\dfrac{3}{4}+\dfrac{6}{5}-\dfrac{1}{4}\)

\(=\dfrac{1}{5}\)

a) \(x+\dfrac{1}{6}=\dfrac{-3}{8}\)

            \(x=\dfrac{-3}{8}-\dfrac{1}{6}\)

           \(x=\dfrac{-13}{24}\)

vậy x =....

b) \(2-\left(\dfrac{3}{4}-x\right)=\dfrac{7}{12}\)

             \(\dfrac{3}{4}-x=2-\dfrac{7}{12}\)

             \(\dfrac{3}{4}-x=\dfrac{17}{12}\)

                    \(x=\dfrac{3}{4}-\dfrac{17}{12}\)

                   \(x=\dfrac{-2}{3}\)

vậy x =....

Câu a: - \(\frac34x\) - 3 = \(\frac14x\)

- \(\frac34x\) - \(\frac14x\) = 3

-\(x=3\)

\(x=3:\left(-1\right)\)

\(x\) = -3

Vậy \(x=-3\)

Câu b:

2,8 : 0,5 = |\(x-1\)| : 1,5

5,6 = |\(x-1\)| : 1,5

|\(x-1\)| = 5,6 x 1,5

|\(x-1\)| = 8,4

\(\left[\begin{array}{l}x-1=-8,4\\ x-1=8,4\end{array}\right.\)

\(\left[\begin{array}{l}x=-8,4+1\\ x=8,4+1\end{array}\right.\)

\(\left[\begin{array}{l}x=-7,4\\ x=9,4\end{array}\right.\)

Vậy \(x\in\) {-7;4 ;9,4}

\(0,5x-\frac{2}{3}x=\frac{5}{2}\)

\(\Rightarrow\frac{1}{2}x-\frac{2}{3}x=\frac{5}{2}\)

\(\Rightarrow x\left(\frac{1}{2}-\frac{2}{3}\right)=\frac{5}{2}\)

\(\Rightarrow x\frac{-1}{6}=\frac{5}{2}\)

\(\Rightarrow x=\frac{5}{2}:\frac{-1}{6}=-15\)

a: ĐKXĐ: 1-x>0

=>x<1

=>TXĐ là D=(-∞;1)

c: ĐKXĐ: \(x^2-x-12>0\)

=>\(x^2-4x+3x-12>0\)

=>(x-4)(x+3)>0

=>x>4 hoặc x<-3

Vậy: TXĐ là D=(4;+∞)\(\cup\) (-∞;-3)

b: ĐKXĐ: \(\frac{2x+1}{x+5}>0\) và \(\log_{0,5}\frac{2x+1}{x+5}-2\ge0\)

=>\(\left[\begin{array}{l}x>-\frac12\\ x<-5\end{array}\right.\) và \(\log_{0,5}\frac{2x+1}{x+5}\ge2\)

=>\(\left[\begin{array}{l}x>-\frac12\\ x<-5\end{array}\right.\) và \(\frac{2x+1}{x+5}\le\frac14\)

=>\(\left[\begin{array}{l}x>-\frac12\\ x<-5\end{array}\right.\) và \(\frac{2x+1}{x+5}-\frac14\le0\)

=>\(\left[\begin{array}{l}x>-\frac12\\ x<-5\end{array}\right.\) và \(\frac{4\left(2x+1\right)-\left(x+5\right)}{4\left(x+5\right)}\le0\)

=>\(\left[\begin{array}{l}x>-\frac12\\ x<-5\end{array}\right.\) và \(\frac{8x+4-x-5}{4\left(x+5\right)}\le0\)

=>\(\left[\begin{array}{l}x>-\frac12\\ x<-5\end{array}\right.\) và \(\frac{7x-1}{x+5}\le0\)

=>\(\left[\begin{array}{l}x>-\frac12\\ x<-5\end{array}\right.\) và \(-5

=>\(-\frac12

=>TXĐ là D=(-1/2;1/7]