\(-15.\left(\chi+2\right)+7.\left(2\chi-3\right)=\left(-5\right).10\)

\(\Rightarrow-15\chi+\left(-30\right)+14\chi-21=-50\)

\(\Rightarrow\left(-15\chi+14\chi\right)=-50+30+21\)

\(\Rightarrow\chi=1\)

HTDT

3) \(-12+2x-9+x=0\\ -21+3x=0\\ 3x=21\\ x=7\)

4)
\(11+\left(15-x\right)=1\)
\(15-x=1-11\)
\(15-x=-10\)
\(x=15-\left(-10\right)\)
\(x=25\)

5) 
\(4-\left(27-3\right)=x-\left(13-4\right)\)
\(4-24=x-9\)
\(x-9=-20\)
\(x=-20+9\)
\(x=-11\)
 

\(3.-12+\left(2x-9\right)+x=0.\)

\(\Leftrightarrow-12+2x-9+x=0.\Leftrightarrow3x=21.\Leftrightarrow x=7.\)

Vậy \(x=7.\)

\(4.11+\left(15-x\right)=1.\Leftrightarrow11+15-x=1.\Leftrightarrow26-x=1.\Leftrightarrow x=25.\)

Vậy \(x=25.\)

\(5.4-\left(27-3\right)=x-\left(13-4\right).\Leftrightarrow4-24=x-9.\Leftrightarrow-20=x-9.\Leftrightarrow x=-11.\)

Vậy \(x=-11.\)

\(6.8-\left(x-10\right)=23-\left(-4+12\right).\Leftrightarrow8-x+10=23-8.\Leftrightarrow18-x=15.\Leftrightarrow x=3.\)

Vậy \(x=3.\)

\(7.105-5\left(10-5x\right)=-20.\Leftrightarrow105-50+25x=-20.\Leftrightarrow25x=-75.\Leftrightarrow x=-3.\)

Vậy \(x=-3.\)

\(8.\left(x-1\right)\left(8-2x\right)\left(3x+123\right)=0.\)

\(\Leftrightarrow\left[{}\begin{matrix}x-1=0.\\8-2x=0.\\3x+123=0.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1.\\x=4.\\x=-41.\end{matrix}\right.\)

Vậy \(x\in\left\{1;4;-41\right\}.\)

\(9.\left(x^2-25\right)\left(x+10\right)=0.\)

\(\Leftrightarrow\left(x-5\right)\left(x+5\right)\left(x+10\right)=0.\)

\(\Leftrightarrow\left[{}\begin{matrix}x-5=0.\\x+5=0.\\x+10=0.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=5.\\x=-5.\\x=-10.\end{matrix}\right.\)

Vậy \(x\in\left\{5;-5;-10\right\}.\)

\(10.x\left(x^2+5\right)=0.\Leftrightarrow x=0.\)

\(\frac{2}{3}.x=\frac{1}{3}\)1) x-\(\frac{10}{3}\)=\(\frac{7}{15}.\frac{3}{5}\)

x-10/3=7/25

x=7/25+10/3

x=\(\frac{271}{75}\)

2)\(\frac{8}{23}.\frac{46}{24}.x=\frac{1}{3}\)

2/3.x=1/3

x=1/3:2/3

x=1/2

( 1/3+1/6+1/10+1/15+1/21) : x =5/7

5/7: x = 5/7

       x = 5/7 : 5/7

       x = 1

tk giùm nhé! chúc học giỏi!

ta có :  ( 1/3 + 1/6 + 1/10 + 1/15 + 1/21 ) :x =5/7

       =>      5/7 : x = 5/7

       => x = 5/7 : 5/7

            x = 1

vậy x=1

( 1/3 + 1/6 + 1/10 +1/15 + 1/21 ) : x = 5/7

                    5/7                       : x = 5/7

                                                 x = 5/7 : 5/7

                                                 x =     1

                                                h cho tớ đi
 

x x - 4/7 = 15/20  

(hình như sai đề, tại vì lớp 4 chưa học lũy thừa)
x * 2/7 -2/3 =1/2

x* 2/7 = 1/2 + 2/3

x* 2/7 = 7/6

x= 7/6 : 2/7

x= 49/12
x : 5/4 + 4/5 =2

x: 5/4 = 2 - 4/5

x: 5/4 = 6/5

x= 6/5 * 5/4

x= 3/2 

4/3 x 7/8 x 5 

= 7/6 x 5

= 35/6
8/9 x 6/5 x 2/3

= 16/15 x 2/3

= 32/45 
4/7 : 5/7 x 10/11

= 4/5 x 10/11

= 8/11
8/13 : 7/13 : 4

= 8/7 : 4

= 2/7

a) \(\dfrac{x}{15}\)=\(\dfrac{x-2}{30}\)

=>30x=15 (x-2)

=>30x=15x-30

=>30x-15x=-30

=>15x =-30

=>x =-2

b)\(\dfrac{7}{8}\)<\(\dfrac{x}{80}\)<\(\dfrac{9}{10}\)

=>\(\dfrac{70}{80}\)<\(\dfrac{x}{80}\)<\(\dfrac{72}{80}\)

=> 70<x<72

=>x=71

c)\(\dfrac{1}{6}\)<\(\dfrac{5}{x}\)<\(\dfrac{1}{4}\)

=>\(\dfrac{5}{30}\)<\(\dfrac{5}{x}\)<\(\dfrac{5}{20}\)

=>20<x<30

=>x={21;22;23;24;25;26;27;28;29}