a)21/4+x=-0,5%

5,25+x=-50

x=-50-5,25

x=-55,25

b)2x²-72=0

2x²=0+72

2x²=72

x²=72/2

x²=36

x=6²=(-6)²

x={6;-6}

a; \(\dfrac{93}{17}\): \(x\) + (- \(\dfrac{21}{17}\)) : \(x\) + \(\dfrac{22}{7}\): \(\dfrac{22}{3}\) = \(\dfrac{5}{14}\)

   \(\dfrac{94}{17}\) \(\times\) \(\dfrac{1}{x}\) - \(\dfrac{21}{17}\) \(\times\) \(\dfrac{1}{x}\) + \(\dfrac{3}{7}\) = \(\dfrac{5}{14}\)

    \(\dfrac{72}{17}\) \(\times\) \(\dfrac{1}{x}\) + \(\dfrac{3}{7}\) = \(\dfrac{5}{14}\)

     \(\dfrac{72}{17x}\)        = \(\dfrac{5}{14}\) - \(\dfrac{3}{7}\)

      \(\dfrac{72}{17x}\)      = - \(\dfrac{1}{14}\)

      17\(x\)       = 72.(-14)

       17\(x\)     = - 1008

         \(x\)       = - 1008 : 17

         \(x\)       = - \(\dfrac{1008}{17}\)

Vậy \(x\) \(=-\dfrac{1008}{17}\)

b; - \(\dfrac{32}{27}\) - (3\(x\) - \(\dfrac{7}{9}\))³ = - \(\dfrac{24}{27}\)

          - \(\dfrac{32}{27}\)  + \(\dfrac{24}{27}\) = (3\(x\) - \(\dfrac{7}{9}\))³ 

          (3\(x-\dfrac{7}{9}\))³ = - \(\dfrac{8}{27}\)

         (3\(x-\dfrac{7}{9}\))³ = (- \(\dfrac{2}{3}\))³

           3\(x-\dfrac{7}{9}\) = - \(\dfrac{2}{3}\)

           3\(x\)        = - \(\dfrac{2}{3}\) + \(\dfrac{7}{9}\)
           3\(x\)        = \(\dfrac{1}{9}\)

             \(x\)        = \(\dfrac{1}{9}\) : 3

             \(x\)       = \(\dfrac{1}{27}\)

Vậy \(x=\dfrac{1}{27}\)

         \(\left(\frac{3}{5}.x-0,75\right):\frac{3}{7}=2\frac{4}{5}\)

\(\Leftrightarrow\)\(\frac{3}{5}.x-0,75=2\frac{4}{5}.\frac{3}{7}=1\frac{1}{5}\)

\(\Leftrightarrow\)\(\frac{3}{5}.x=1\frac{1}{5}+0,75=1,95\)

\(\Leftrightarrow\)\(x=1,95:\frac{3}{5}=3,25\)

Vậy....

Bài 3:

a: \(\frac13+\frac23:x=-7\)

=>\(\frac23:x=-7-\frac13=-\frac{22}{3}\)

=>\(x=\frac23:\frac{-22}{3}=\frac{-2}{22}=-\frac{1}{11}\)

b: \(3\frac12-\frac12x=\frac23\)

=>\(\frac72-\frac{x}{2}=\frac13\)

=>\(7-x=\frac23\)

=>\(x=7-\frac23=\frac{21}{3}-\frac23=\frac{19}{3}\)

c: \(\left\lbrack\left(x+\frac13\right)\cdot\frac34+5\right\rbrack:2=3\)

=>\(\left(x+\frac13\right)\cdot\frac34+5=3\cdot2=6\)

=>\(\left(x+\frac13\right)\cdot\frac34=1\)

=>\(x+\frac13=1:\frac34=\frac43\)

=>\(x=\frac43-\frac13=\frac33=1\)

d: \(\left(1\frac23-x\right)\cdot0,75-2=\frac12\)

=>\(\left(\frac53-x\right)\cdot\frac34=2+\frac12=\frac52\)

=>\(\frac53-x=\frac52:\frac34=\frac52\cdot\frac43=\frac{5\cdot2}{3}=\frac{10}{3}\)

=>\(x=\frac53-\frac{10}{3}=-\frac53\)

e: \(x+75\%\cdot x=-1,6\)

=>\(x+0,75x=-1,6\)

=>1,75x=-1,6

=>\(x=-\frac{160}{175}=-\frac{32}{35}\)

f: \(\left(x-\frac23\right)\left(2x+1\right)=0\)

=>\(\left[\begin{array}{l}x-\frac23=0\\ 2x+1=0\end{array}\right.\Rightarrow\left[\begin{array}{l}x=\frac23\\ x=-\frac12\end{array}\right.\)

g: \(1-\left(2x+\frac12\right)^2=\frac34\)

=>\(\left(2x+\frac12\right)^2=1-\frac34=\frac14\)

=>\(\left[\begin{array}{l}2x+\frac12=\frac12\\ 2x+\frac12=-\frac12\end{array}\right.\Rightarrow\left[\begin{array}{l}2x=\frac12-\frac12=0\\ 2x=-\frac12-\frac12=-1\end{array}\right.\Rightarrow\left[\begin{array}{l}x=0\\ x=-\frac12\end{array}\right.\)

h: \(\frac{5}{1\cdot6}+\frac{5}{6\cdot11}+\cdots+\frac{5}{\left(5x+1\right)\left(5x+6\right)}=\frac{2020}{2021}\)

=>\(1-\frac16+\frac16-\frac{1}{11}+\cdots+\frac{1}{5x+1}-\frac{1}{5x+6}=\frac{2020}{2021}\)

=>\(1-\frac{1}{5x+6}=\frac{2020}{2021}\)

=>\(\frac{1}{5x+6}=\frac{1}{2021}\)

=>5x+6=2021

=>5x=2015

=>x=403

a) x² - 4x = 0

<=> x(x - 4) = 0

<=> x = 0 hoặc x - 4 = 0

<=> x = 0 hoặc x = 4

b) 4x - (3 + 5x) = 14

<=> 4x - 3 - 5x = 14

<=> - x = 14 +3

<=> - x = 17

=> x = - 17

c)\(\frac{-7^5.3^3}{7^2.\left(-3\right)^3}=\frac{-7^5.3^3}{-7^2.3^3}=\frac{7^5}{7^2}=7^3=343\)

Bài 1: 

1: =-5/24+16/27+3/4

=-5/24+18/24+16/27

=13/24+16/27

=117/216+128/216=245/216

2: =-1/3+1/3+6/7=6/7

3: \(=\dfrac{1}{2}-\dfrac{7}{12}+\dfrac{1}{2}=1-\dfrac{7}{12}=\dfrac{5}{12}\)

4: \(=-\dfrac{5}{8}+\dfrac{14}{25}-\dfrac{6}{10}=\dfrac{-125+112-120}{200}=\dfrac{-133}{200}\)

\(a,5x-5\left(-3\right)=15\)

\(\Leftrightarrow5x+15=15\)

\(\Leftrightarrow5x=0\)

\(\Leftrightarrow0\)

\(b,x=\frac{18.36.\left(-119\right)}{12.9.17}\)

\(=\frac{2.3^2.2^2.3^2.\left(-7\right).17}{2^2.3.17}\)

\(=\frac{-2^3.3^4.7.17}{2^2.3.17}\)

\(=-2.3^3.7\)