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x=(3,15.0,15): 7,2

x=\(\frac{21}{320}\)

Chúc thành công.

Có : \(\frac{x}{3,15}=\frac{0,15}{7,2}\Rightarrow x=\frac{0,15.3,15}{7,2}=\frac{21}{320}\)

\(\frac{x}{3,15}=\frac{0,15}{7,2}\)

\(\Rightarrow x.7,2=3,15.0,15\)

\(\Rightarrow x.7,2=\frac{189}{400}\)

\(\Rightarrow x=\frac{189}{400}:7,2\)

\(\Rightarrow x=\frac{21}{320}\)

Vậy \(x=\frac{21}{320}.\)

Chúc bạn học tốt!

\(a.\) \(\frac{x}{3.15}\) \(=\) \(\frac{0.15}{7.2}\) 

<=> \(x=\) \(\frac{0.15\cdot3.15}{7.2}\) 

<=>\(x=0.065625\)

\(b.\) \(\frac{-2.6}{x-11}=\frac{-12}{42}\) 

<=>\(x-11=\frac{-2.6\cdot-12}{42}\)

<=>\(x-11=0.742857142\)

<=>\(x=11.74285714\)

\(3\frac{4}{5}:2x=0,25:2\frac{2}{3}\)

\(\Leftrightarrow\frac{19}{5}:2x=0,25:\frac{8}{3}\)

\(\Leftrightarrow\frac{19}{5}:2x=0,25\cdot\frac{3}{8}\)

\(\Leftrightarrow\frac{19}{5}:2x=\frac{3}{32}\)

\(\Leftrightarrow2x=\frac{19}{5}:\frac{3}{32}=\frac{19}{5}\cdot\frac{32}{3}=\frac{608}{15}\)

\(\Leftrightarrow x=\frac{608}{15}:2=\frac{608}{30}=\frac{304}{15}\)

\(a,-\dfrac{3}{5}-x=-0,75\\ -\dfrac{3}{5}-x=-\dfrac{3}{4}\\ x=-\dfrac{3}{5}-\left(-\dfrac{3}{4}\right)\\ x=-\dfrac{3}{5}+\dfrac{3}{4}=\dfrac{3}{20}\\ ---\\ b,1\dfrac{4}{5}=-0,15-x\\ \dfrac{9}{5}=-\dfrac{3}{20}-x\\ x=-\dfrac{3}{20}-\dfrac{9}{5}\\ x=-\dfrac{3}{20}-\dfrac{36}{20}\\ x=-\dfrac{39}{20}\\ ----\\ c,2\dfrac{1}{2}-x+\dfrac{4}{5}=\dfrac{2}{3}-\left(-\dfrac{4}{7}\right)\\ \dfrac{5}{2}-x+\dfrac{4}{5}=\dfrac{2}{3}+\dfrac{4}{7}\\ \dfrac{33}{10}-x=\dfrac{26}{21}\\ x=\dfrac{33}{10}-\dfrac{26}{21}\\ x=\dfrac{433}{210}\)

a)\(\) Ta có : x / 3,15  =  0,15 / 7,2

            (=)  x = 0,15 . 3,15 / 7,2   

                     = 21 / 320

b)    Ta có : -2,6 / x = -12 / 42

             (=) x = -2,6 . 42 / -12

                     = 91 / 10                                                                                 

a) => x . 7,2 = 0,15 . 3,15

=> x . 7,2 =0,4725

=> x = 0,4725 : 7,2 =21/320

b) => x . 25x = 6.24 

=> 25 . x² =144

=> x² = 144 : 25 =144/25

=> x= 12/5 hoặc -12/5 hoặc 12/-5

c) => 1/5:x =8/3

=> x = 1/5 :8/3 =3/40

d) => x-1 = 6,7 . ( x+5)

=> x-1 = 6,7x+33,5

=> x-6,7x = 33,5+1 =34,5

=> x ( 1-6,7) = 34,5

=> -5,7 x = 34,5

=> x = 34,5 : (-5,7) =-115/19

a) \(-\dfrac{3}{5}-x=-0,75\)

\(\Rightarrow-\dfrac{3}{5}-x=-\dfrac{3}{4}\)

\(\Rightarrow x=\dfrac{3}{4}-\dfrac{3}{5}\)

\(\Rightarrow x=\dfrac{15}{20}-\dfrac{12}{20}=\dfrac{8}{20}=\dfrac{2}{5}\)

b) \(1\dfrac{4}{5}=-0,15-x\)

\(\Rightarrow\dfrac{9}{5}=-\dfrac{3}{20}-x\)

\(\Rightarrow x=-\dfrac{3}{20}-\dfrac{9}{5}\)

\(\Rightarrow x=-\dfrac{3}{20}-\dfrac{36}{20}=-\dfrac{39}{20}\)

c) \(x+\dfrac{1}{3}=\dfrac{2}{5}-\left(-\dfrac{1}{3}\right)\)

\(\Rightarrow x+\dfrac{1}{3}=\dfrac{2}{5}+\dfrac{1}{3}\)

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

a) \(-\dfrac{3}{5}-x=-0,75\)

\(x=-\dfrac{3}{5}+0,75=\dfrac{3}{5}+\dfrac{3}{4}\)

\(x=\dfrac{27}{20}\)

________

b) \(1\dfrac{4}{5}=-0,15-x\)

\(=>-0,15-x=\dfrac{9}{5}\)

\(x=\dfrac{-3}{20}-\dfrac{9}{5}=\dfrac{-3}{20}-\dfrac{36}{20}\)

\(x=\dfrac{-39}{20}\)

c) \(x+\dfrac{1}{3}=\dfrac{2}{5}-\left(-\dfrac{1}{3}\right)=\dfrac{6}{15}+\dfrac{5}{15}\)

\(x+\dfrac{1}{3}=\dfrac{11}{15}\)

\(x=\dfrac{11}{15}-\dfrac{1}{3}=\dfrac{11}{15}-\dfrac{5}{15}\)

\(x=\dfrac{6}{15}=\dfrac{2}{5}\)

Mik sửa lại câu a

\(...x=-\dfrac{3}{5}--0,75=\dfrac{-3}{5}+\dfrac{3}{4}\)

\(x=\dfrac{-12}{20}+\dfrac{15}{20}\)

\(x=\dfrac{3}{20}\)

\(a,\Leftrightarrow\dfrac{9}{5}=-\dfrac{3}{20}-x\\ \Leftrightarrow-\dfrac{9}{5}=x+\dfrac{3}{20}\\ \Leftrightarrow x=-\dfrac{9}{5}-\dfrac{3}{20}=-\dfrac{39}{20}\\ b,\Leftrightarrow-x+2x=\dfrac{3}{5}+\dfrac{4}{7}\\ \Leftrightarrow x=\dfrac{41}{35}\\ c,\Leftrightarrow\dfrac{3}{8}-\dfrac{1}{5}+\dfrac{5}{8}-x=\dfrac{1}{5}\\ \Leftrightarrow1-x=\dfrac{2}{5}\\ \Leftrightarrow x=1-\dfrac{2}{5}=\dfrac{3}{5}\)

Giúp mình với 

a: Ta có: \(-x-\dfrac{3}{20}=\dfrac{9}{5}\)

\(\Leftrightarrow x=-\dfrac{9}{5}+\dfrac{3}{20}=\dfrac{-36+3}{20}=\dfrac{-33}{20}\)

b: Ta có: \(\dfrac{-4}{7}-x=\dfrac{3}{5}-2x\)

\(\Leftrightarrow x=\dfrac{3}{5}+\dfrac{4}{7}=\dfrac{41}{35}\)