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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
\(\frac{11}{13}-\left(\frac{5}{42}-x\right)=-\left(\frac{15}{28}-\frac{11}{13}\right)\)
\(=\frac{11}{13}-\left(\frac{5}{42}-x\right)=\frac{113}{364}\)
\(\Rightarrow\frac{5}{42}-x=\frac{11}{13}-\frac{113}{364}\)
\(\Rightarrow x=\frac{5}{42}-\frac{15}{28}\)
\(\Rightarrow x=\frac{-5}{12}\)
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
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 = \(x\)
11/12-(5/42-x)=-(15-11/13)
=>11/13-(5/42-x)=184/13
=>5/42-x=11/13- (-184/13)
=>5/42-x=15
=>x=5/42-15
=>x=-625/42
5/42-x=11/13- [-(15-11/13)]=11/13+15-11/13
5/42-x=(11/13-11/13)+15=15
x=5/42-15=5/42-630/42
x=-625/42
Vậy x=-625/42
\(\frac{11}{13}-\left(\frac{5}{42}-x\right)=-\left(\frac{15}{28}-\frac{11}{13}\right)\)
\(\frac{11}{13}-\frac{5}{42}+x=-\frac{15}{28}+\frac{11}{13}\)
\(\frac{-5}{42}+x=-\frac{15}{28}+\left(\frac{11}{13}-\frac{11}{13}\right)\)
\(\frac{-5}{42}+x=-\frac{15}{28}\)
\(x=-\frac{15}{28}+\frac{5}{42}\)
\(x=-\frac{45}{84}+\frac{10}{84}\)
\(x=-\frac{35}{84}\)
Vậy \(x=-\frac{35}{84}\).
\(\frac{11}{13}-\left(\frac{5}{42}-x\right)=\frac{113}{364}\)
\(\left(\frac{5}{42}-x\right)=\frac{11}{13}-\frac{113}{364}\)
\(\left(\frac{5}{42}-x\right)=\frac{15}{28}\)
\(x=\frac{5}{42}-\frac{15}{28}\)
\(x=-\frac{5}{12}\)
vậy \(x=-\frac{5}{12}\)