Bài làm:

a) \(\left(\frac{2x}{7}-5\right)\div\left(-8\right)=0,75\)

\(\Leftrightarrow\frac{2x}{7}-5=-6\)

\(\Leftrightarrow\frac{2x}{7}=-1\)

\(\Leftrightarrow x=-\frac{7}{2}\)

b) \(\frac{11}{13}-\left(\frac{5}{42}-x\right)=-\left(\frac{15}{28}-\frac{11}{13}\right)\)

\(\Leftrightarrow x+\frac{11}{13}-\frac{5}{42}=\frac{11}{13}-\frac{15}{28}\)

\(\Rightarrow x=-\frac{5}{7}\)

\(\frac{11}{13}-\left(\frac{5}{42}-x\right)=\frac{113}{364}\)

\(\left(\frac{5}{42}-x\right)=\frac{11}{13}-\frac{113}{364}\)

\(\left(\frac{5}{42}-x\right)=\frac{15}{28}\)

\(x=\frac{5}{42}-\frac{15}{28}\)

\(x=-\frac{5}{12}\)

vậy \(x=-\frac{5}{12}\)

\(\frac{1}{13}-\left(\frac{5}{42}-x\right)=-\left(-\frac{113}{364}\right)\)

=>\(\frac{1}{13}-\frac{5}{42}+x=\frac{113}{364}\)

=>\(-\frac{23}{546}+x=\frac{113}{364}\)

=>\(x=\frac{113}{364}-\left(-\frac{23}{546}\right)\)

=>\(x=\frac{113}{364}+\frac{23}{546}\)

=>\(x=\frac{55}{156}\)

a ) | x + 1/3 | = 5/6

+) x + 1/3 = 5/6            hay     x + 1/3 = -5/6

    x          = 5/6 - 1/3              x          = -5/6 - 1/3

    x          = 1/2                     x           =-7/6

b ) 11/13 - ( 5/42 - x ) = - ( 15/28-11/13 )

      11/13 - ( 5/42 - x ) = 113/364

                 ( 5/42 - x ) = 11/13 - 113/364

                 ( 5/42 - x ) = 15/28

                            x   = 5/42 - 15/28

                            x  = -5/12

c ) | x |/186 = ( 1 - 303030 / 313131 ) + ( 616161 / 626262 - 1 )

     | x | / 186 = 1/62

     | x |          = 1/62 . 186

     | x |          = 3

       x            = 3 hoặc -3

\(\frac{11}{13}-\left(\frac{5}{42}-x\right)=-\left(\frac{15}{28}-\frac{11}{13}\right)\)

\(\left(\frac{5}{42}-x\right)=\frac{11}{13}-\left(-\frac{15}{28}-\frac{11}{13}\right)\)

\(\frac{5}{42}-x\)= \(\frac{11}{13}-\left(-\frac{503}{364}\right)\)

\(\frac{5}{42}-x\)= \(\frac{811}{364}\)

\(x=\frac{5}{42}-\frac{811}{364}\)

\(x=-\frac{329}{156}\)

Phần tìm x tự tính ra

xin lỗi, tui lp 6

X = - 5 / 12

\(\frac{11}{13}-\left(\frac{5}{42}-x\right)=-\left(\frac{15}{28}-\frac{11}{13}\right)\)

\(=\frac{11}{13}-\left(\frac{5}{42}-x\right)=\frac{113}{364}\)

\(\Rightarrow\frac{5}{42}-x=\frac{11}{13}-\frac{113}{364}\)

\(\Rightarrow x=\frac{5}{42}-\frac{15}{28}\)

\(\Rightarrow x=\frac{-5}{12}\)

\(\frac{11}{13}-\left(\frac{5}{42}-x\right)=-\left(\frac{15}{28}-\frac{11}{13}\right)\)

<=> \(\frac{11}{13}-\frac{5}{42}+x=-\left(-\frac{113}{364}\right)\)

<=> \(\frac{397}{546}+x=\frac{113}{364}\)

<=> \(x=\frac{-5}{12}\)

học tốt

A)  7/38 x 9/11 +7/38 x 4/11 -7/38 x 2/11

=7/38.(9/11+4/11-2/11)

=7/38

B) 5/31 x 21/25 + 5/31 x -7/10 - 5/31 x 9/20

=5/31.(21/25-7/10-9/20)

=5/31.(-31/100)

=-1/20

NHANH NHANH GIÚP MÌNH VỚI NHÉ MÌNH ĐANG CẦN GẤP 

Bài 7:

a, \(x\) = \(\dfrac{1}{5}\) + \(\dfrac{2}{11}\)

    \(x\) = \(\dfrac{11}{55}\) + \(\dfrac{10}{55}\)

     \(x=\dfrac{21}{55}\)

b, \(\dfrac{x}{15}\) = \(\dfrac{3}{5}\) - \(\dfrac{2}{3}\)

    \(\dfrac{x}{15}\) = \(\dfrac{9}{15}\) - \(\dfrac{10}{15}\)

      \(\dfrac{x}{15}\) = \(\dfrac{1}{15}\)

      \(x\) = 1

c, \(\dfrac{11}{8}\) + \(\dfrac{13}{6}\)= \(\dfrac{85}{x}\)

     \(\dfrac{33}{24}\) + \(\dfrac{52}{24}\) = \(\dfrac{85}{x}\)

       \(\dfrac{85}{24}\) = \(\dfrac{85}{x}\)

        24 = \(x\)

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