\(\frac{-2}{7}\div\frac{15}{14}=\frac{-21}{20}\div\left(5\times x\right)\)

\(\Rightarrow\frac{-4}{15}=\frac{-21}{20}\div\left(5\times x\right)\)

\(\Rightarrow5\times x=\frac{-21}{20}\div\frac{-4}{15}\)

\(\Rightarrow5\times x=\frac{63}{16}\)

\(\Rightarrow x=\frac{63}{16}\div5\)

\(\Rightarrow x=\frac{63}{80}\)

~ học tốt nha ~

\(\frac{-2}{7}:\frac{15}{14}=\frac{-21}{20}:(5\cdot x)\)

\(\Leftrightarrow\frac{-21}{20}:(5\cdot x)=\frac{-2}{7}:\frac{15}{14}\)

\(\Leftrightarrow\frac{-21}{20}:(5\cdot x)=\frac{-2}{7}\cdot\frac{14}{15}\)

\(\Leftrightarrow\frac{-21}{20}:(5\cdot x)=\frac{-2}{1}\cdot\frac{2}{15}\)

\(\Leftrightarrow\frac{-21}{20}:(5\cdot x)=\frac{4}{15}\)

\(\Leftrightarrow5\cdot x=\frac{-21}{20}:\frac{4}{15}\)

\(\Leftrightarrow5\cdot x=\frac{-21}{20}\cdot\frac{15}{4}\)

\(\Leftrightarrow5\cdot x=\frac{-21}{4}\cdot\frac{3}{4}\)

\(\Leftrightarrow5\cdot x=\frac{-63}{16}\)

\(\Leftrightarrow x=\frac{-63}{16}:5\)

\(\Leftrightarrow x=\frac{-63}{16}\cdot\frac{1}{5}=\frac{-63}{80}\)

dòng thứ tư xuống dòng 5 bạn Tiêu Chiến tính sai rồi nha

tính trừ bt nha bạn vế thương thì cũng tĩnh ra xong mới tính nha

a, \(x\) + \(\dfrac{1}{4}\) - \(\dfrac{3}{8}\) = \(\dfrac{7}{12}\)

    \(x\) - \(\dfrac{1}{8}\) = \(\dfrac{7}{12}\)

    \(x\)       = \(\dfrac{7}{12}\) + \(\dfrac{1}{8}\)

     \(x\)      = \(\dfrac{17}{24}\)

b, \(x\) - \(\dfrac{3}{14}\) = \(\dfrac{5}{14}\) + \(\dfrac{15}{21}\)

    \(x\)  - \(\dfrac{3}{14}\) = \(\dfrac{15}{14}\)

    \(x\)          = \(\dfrac{15}{14}\) + \(\dfrac{3}{14}\)

     \(x\)         = \(\dfrac{9}{7}\)

a)-7x+7=21                                          

-7x=21-7

-7x=16

x=16:-7

x=-16/7

\(a,-7x+7=21\)

\(\Rightarrow-7x=21-7=14\)

\(\Rightarrow x=-2\)

\(b,9x+11=20x+66\)

\(\Rightarrow9x-20x=66-11=55\)

\(\Rightarrow-11x=55\)

\(\Rightarrow x=-5\)

\(c,3^3.x+4^2=5^2.x-2.\left(2017\right)^0\)

\(27x+16=25x-2\)

\(\Rightarrow16+2=25x-27x=-2x\)

\(\Rightarrow-2x=18\)

\(\Rightarrow x=-9\)

\(d,\left(2+3+...+20\right)x=2100\)

\(\Rightarrow\frac{\left(20+2\right)\left[\left(20-2\right):1+1\right]}{2}x=2100\)

\(11.19.x=2100\)

\(\Rightarrow x\simeq10\)

\(e,5\left(\left|x\right|-14\right)=10\)

\(\Rightarrow\left|x\right|-14=10:5=2\)

\(\Rightarrow\left|x\right|=16\)

\(\Rightarrow x=\orbr{\begin{cases}16\\-16\end{cases}}\)

a) \(\dfrac{7}{-25}+\dfrac{8}{25}=\dfrac{-7}{25}+\dfrac{8}{25}=\dfrac{1}{25}\)

\(\dfrac{4}{5}+\dfrac{4}{-18}=\dfrac{4}{5+\left(-18\right)}=\dfrac{4}{-13}=\dfrac{-4}{13}\)

\(\dfrac{7}{21}+\dfrac{9}{-36}=\dfrac{1}{3}+\dfrac{1}{-4}=\dfrac{1}{3+\left(-4\right)}=\dfrac{1}{-1}=1\)

b) \(\dfrac{12}{20}-\dfrac{2}{5}=\dfrac{12}{20}+\left(\dfrac{-2}{5}\right)=\dfrac{3}{5}+\dfrac{-2}{5}=\dfrac{3+\left(-2\right)}{5}=\dfrac{1}{5}\)

\(\dfrac{2}{3}-\dfrac{-5}{6}=\dfrac{2}{3}+\dfrac{5}{6}=\dfrac{4}{6}+\dfrac{5}{6}=\dfrac{9}{6}=\dfrac{3}{2}\)

\(6-\dfrac{3}{20}=6+\dfrac{-3}{20}=\dfrac{60}{60}+\dfrac{-9}{60}=\dfrac{51}{60}\)

c) \(\dfrac{2}{21}.\dfrac{-7}{3}=\dfrac{2.\left(-1\right)}{7.3}=\dfrac{-2}{21}\)

\(\dfrac{27}{28}.\left(-21\right)=\dfrac{27.\left(-21\right)}{28}=\dfrac{-567}{28}\)

\(\dfrac{-15}{7}.\dfrac{-14}{25}=\dfrac{-3.\left(-2\right)}{1.5}=\dfrac{6}{5}\)

a, 5/-14. 7/-19=8/38

b, -15/4 .( 16/-25 )=12/5

c, 3/-10 .( -15/-2 )=

d, -5/7 . ( 21/-10 )=-9/4

e, 10/-3. (6/-5)==4

f, 21/-9 . ( -6/14 )=1

g, -10/9 . ( 36/20 )=-2

1/3(2x-5)=-2/3-3/2=-13/6

2x-5=-13/6:1/3=-13/2

2x=-13/2+5

2x=-3/2

x=-3/2:2=-3/4

       Trương Ứng Hòa

Conan bn sai rùi nhé tại sao chỉ còn 1/3 ? còn (-1/3)chứ

\(\frac{X}{2}=\frac{Y}{3}=\frac{Z}{4}\)\(=\frac{X}{2}=\frac{2Y}{6}=\frac{3Z}{12}\)\(=\frac{X+2Y-3Z}{2+6-12}\)\(=5\)

\(=>X=2.5=10\)

\(=>y=3.5=15\)

\(=>z=4.5=20\)

vậy.....

Bài 1:

a) \(\frac{16}{15}.\frac{\left(-5\right)}{14}.\frac{54}{24}.\frac{56}{21}\)

\(=\frac{4.2.2}{5.3}.\frac{\left(-5\right)}{2.7}.\frac{3.3}{4}.\frac{8}{3}\)

\(=\frac{4.2.2.\left(-5\right).3.3.8}{5.3.2.7.4.3}\)

\(=\frac{-16}{7}\)

b) \(\frac{7}{3}.\frac{\left(-5\right)}{2}.\frac{15}{21}.\frac{4}{\left(-5\right)}\)

\(=\frac{7}{3}.\frac{\left(-5\right)}{2}.\frac{5}{7}.\frac{2.2}{\left(-5\right)}\)

\(=\frac{7.\left(-5\right).5.2.2}{3.2.7.\left(-5\right)}\)

\(=\frac{10}{3}\)

Bài 2:

a) \(\frac{21}{24}.\frac{11}{9}.\frac{5}{7}=\frac{7}{8}.\frac{11}{9}.\frac{5}{7}=\frac{11.5}{8.9}=\frac{55}{72}\)

b) \(\frac{5}{23}.\frac{17}{26}+\frac{5}{23}.\frac{9}{26}\)

\(=\frac{5}{23}.\left(\frac{17}{26}+\frac{9}{26}\right)=\frac{5}{23}.1=\frac{5}{23}\)

c) \(\left(\frac{3}{29}-\frac{1}{5}\right).\frac{29}{3}=\frac{3}{29}.\frac{29}{3}-\frac{1}{5}.\frac{29}{3}\)

\(=1-1\frac{14}{15}=\frac{14}{15}\)

Bài 3:

a) x/5 = 2/5

=> x =2

b) -4/x = 20/14 = 10/7

=> -4/x = 10/7

=> x.10 = (-4).7

x.10 = - 28

x= -28 :10

x= -2,8

c) 4/7 = 12/x = 12/ 21

=> 12/x = 12/21

=> x = 21

d) 3/7 = x / 21 = 9/21

=> x/21 = 9/21

=> x= 9