a, \(=16,24\left(12-3+1\right)\)

\(=16,24.10=162,4\)

b, \(=1,25\left(1+2+7\right)\)

\(=1,25.10=12,5\)

c, \(=2,46\left(2+8\right)\)

\(=2,46.10=24,6\)

\(a,=16,24\times12-16,24\times3+16,24\times1\\ =16,24\times\left(12-3+1\right)=16,24\times10=162,4\\ b,=1,25\times\left(1+2+7\right)=1,25\times10=12,5\)

a 16.24( 12-10+3)=16.24 x 5=81.2

b  1.25(1+2+7)=1.25 x 10= 12.5

c  2.46 x 2 + 2.46 x8 = 2.46(2 + 8)=2.46 x 10=24.6

a) \(\dfrac{2}{3}x-\dfrac{1}{2}x=\left(-\dfrac{7}{12}\right)\cdot1\dfrac{2}{5}\)

\(\Rightarrow\dfrac{1}{6}x=\left(-\dfrac{7}{12}\right)\cdot\dfrac{7}{5}\)

\(\Rightarrow\dfrac{1}{6}x=-\dfrac{49}{60}\)

\(\Rightarrow x=-\dfrac{49}{60}:\dfrac{1}{6}\)

\(\Rightarrow x=-\dfrac{49}{10}\) 

b) \(\left(\dfrac{1}{5}-\dfrac{3}{2}x\right)^2=\dfrac{9}{4}\)

\(\Rightarrow\left(\dfrac{1}{5}-\dfrac{3}{2}x\right)^2=\left(\pm\dfrac{3}{2}\right)^2\)

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

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

\(\Rightarrow\dfrac{3}{2}x=-\dfrac{13}{10}\)

\(\Rightarrow x=-\dfrac{13}{10}:\dfrac{3}{2}\)

\(\Rightarrow x=-\dfrac{13}{15}\)

+) \(\left(1,25-\dfrac{4}{5}x\right)^3=-125\)

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

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

\(\Rightarrow\dfrac{4}{5}x=\dfrac{5}{4}+5\)

\(\Rightarrow\dfrac{4}{5}x=\dfrac{25}{4}\)

\(\Rightarrow x=\dfrac{25}{4}:\dfrac{4}{5}\)

\(\Rightarrow x=\dfrac{125}{16}\)

a, \(\dfrac{2}{3}\)\(x\) - \(\dfrac{1}{2}\)\(x\) = (- \(\dfrac{7}{12}\)). 1\(\dfrac{2}{5}\)

    \(x\).(\(\dfrac{2}{3}\) - \(\dfrac{1}{2}\)) = (- \(\dfrac{7}{12}\)) . \(\dfrac{7}{5}\)

    \(x\). \(\dfrac{1}{6}\) = - \(\dfrac{49}{60}\)

    \(x\)      = - \(\dfrac{49}{60}\).6

    \(x\)      = -\(\dfrac{49}{10}\)

Bài 1: Tìm \(x\) 

a; \(x-2\) + 7 = 1.3.(-9)

   \(x\) - 2 + 7 = 3.(-9)

   \(x\) - 2 + 7 = - 27

  \(x\)             = - 27 - 7 + 2

   \(x\)            = - 34 + 2

   \(x\)            = - 32

Vậy \(x=-32\)

Bài 1

c; - 2\(x\) + 5 = 7

     - 2\(x\)       = 7  - 5

    - 2\(x\)        = - 2

        \(x\)        = -2 : (-2)

        \(x\)        = - 1

Vậy \(x\)         = - 1

Bài 1 b; d xem lại đề bài xem chỗ trống giữa các số là dấu gì!

25/2

181/5

247/2

71/5

a)`1,25 + 1,25 xx 2 + 7 xx 1,25=1,25 xx (1+2+7) = 1,25 xx 10 =12,5`

b)`3,62xx12–2xx0,362xx10=3,62 xx 12 -2 xx 3,62=3,62xx(12-2)=3,62xx10=36,2`

c)`12,35xx15–1,235xx10xx6+12,35=12,35xx15–12,35xx6+12,35=12,35xx(15-6+1)=12,35xx10=123,5`    

d)`1,42 : 0,5 + 1,42 xx 8=1,42xx2+1,42xx8=1,42xx(2+8)=1,42xx10=14,2`

a: \(=\dfrac{15}{4}:\dfrac{2-7}{16}-\dfrac{5}{9}\cdot\left(\dfrac{3}{5}+\dfrac{4}{5}\right)\)

\(=\dfrac{15}{4}\cdot\dfrac{16}{-5}-\dfrac{5}{9}\cdot\dfrac{7}{5}\)

\(=\dfrac{-240}{20}-\dfrac{7}{9}=-12-\dfrac{7}{9}=\dfrac{-115}{9}\)

c: \(=\dfrac{1}{5}-\dfrac{7}{2}-\dfrac{3}{2}+\dfrac{5}{4}\)

\(=\dfrac{4+25}{20}-5=\dfrac{29}{20}-\dfrac{100}{20}=\dfrac{-71}{20}\)

d: \(=\dfrac{12}{17}\left(1-\dfrac{1}{15}-\dfrac{4}{5}+1\right)=\dfrac{12}{17}\cdot\dfrac{17}{15}=\dfrac{12}{15}=\dfrac{4}{5}\)

e: \(=\dfrac{2}{15}\cdot\dfrac{9}{8}-\dfrac{7}{4}\cdot\dfrac{9}{8}+\dfrac{25}{36}\)

\(=\dfrac{9}{8}\left(\dfrac{2}{15}-\dfrac{7}{4}\right)+\dfrac{25}{36}\)

\(=\dfrac{9}{8}\cdot\dfrac{8-105}{60}+\dfrac{25}{36}\)

\(=\dfrac{9}{8}\cdot\dfrac{-97}{60}+\dfrac{25}{36}=\dfrac{-1619}{1440}\)