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25 tháng 6 2018

a) \(\frac{18}{45}-\frac{4}{12}-\frac{6}{9}-\frac{21}{35}=\frac{2}{5}-\frac{1}{3}-\frac{2}{3}-\frac{3}{5}\)

\(=\left(\frac{2}{5}-\frac{3}{5}\right)-\left(\frac{1}{3}+\frac{2}{3}\right)\)

\(=\frac{-1}{3}-1\)

\(=\frac{-4}{3}\)

b) \(\frac{4}{3}+\frac{3}{5}+\frac{7}{3}+\frac{2}{5}+\frac{1}{3}=\left(\frac{4}{3}+\frac{7}{3}+\frac{1}{3}\right)+\left(\frac{3}{5}+\frac{2}{5}\right)\)

\(=4+1=5\)

c) \(\frac{1}{3}.\frac{4}{5}.\frac{1}{3}.\frac{6}{5}=\frac{8}{75}\)

d) \(\frac{6}{7}.\frac{8}{13}+\frac{6}{7}.\frac{9}{13}-\frac{3}{13}.\frac{6}{7}\)

\(=\frac{6}{7}.\left(\frac{8}{13}+\frac{9}{13}-\frac{3}{13}\right)\)

\(=\frac{6}{7}.\frac{14}{13}\)

\(=\frac{12}{13}\)

27 tháng 9 2017

to lắm đây là bài tự nghĩ ra đúng ko

2: \(=\dfrac{-2}{75}+\dfrac{5}{39}=\dfrac{33}{325}\)

3: \(=\dfrac{6}{11}\left(\dfrac{4}{9}+\dfrac{5}{9}\right)=\dfrac{6}{11}\)

4: \(=\dfrac{7}{19}\left(\dfrac{5}{13}+\dfrac{8}{13}-1\right)=-2\cdot\dfrac{7}{19}=-\dfrac{14}{19}\)

5: \(=\dfrac{2}{7}\left(\dfrac{4}{23}-\dfrac{27}{23}+1\right)=0\)

6: \(=\dfrac{3}{8}\left(\dfrac{3}{7}+\dfrac{4}{7}\right)+\dfrac{11}{8}=\dfrac{3}{8}+\dfrac{11}{8}=\dfrac{14}{8}=\dfrac{7}{4}\)

Bài 1:

a: \(x=\dfrac{2}{3}:\dfrac{3}{5}=\dfrac{2}{3}\cdot\dfrac{5}{3}=\dfrac{10}{9}\)

b: \(x=\dfrac{17}{8}:\dfrac{7}{17}=\dfrac{17}{8}\cdot\dfrac{17}{7}=\dfrac{289}{56}\)

c: \(x=-\dfrac{3}{4}:\dfrac{7}{12}=\dfrac{-3}{4}\cdot\dfrac{12}{7}=\dfrac{-63}{28}=-\dfrac{9}{4}\)

d: \(\Leftrightarrow x\cdot\dfrac{1}{6}=\dfrac{3}{8}-\dfrac{1}{4}=\dfrac{1}{4}\)

hay \(x=\dfrac{1}{4}:\dfrac{1}{6}=\dfrac{3}{2}\)

e: \(\Leftrightarrow\dfrac{1}{2}:x=-4-\dfrac{1}{3}=-\dfrac{17}{3}\)

hay \(x=-\dfrac{1}{2}:\dfrac{17}{3}=\dfrac{-3}{34}\)

27 tháng 7 2023

dad

25 tháng 6 2017

a) \(6-2\left(x+4\right)=-4\)

\(\Leftrightarrow6-2x-8=-4\)

\(\Leftrightarrow-2-2x=-4\)

\(\Leftrightarrow-2x=-4+2\)

\(\Leftrightarrow-2x=-2\)

\(\Leftrightarrow x=1\)

Vậy \(x=1\)

b) tự làm.

c) \(2x-15:5=-7\)

\(\Leftrightarrow2x-7,5=-7\)

\(\Leftrightarrow2x=-7+7,5\)

\(\Leftrightarrow2x=0,5\)

\(\Leftrightarrow x=0,25\)

\(\Leftrightarrow x=\dfrac{1}{4}\)

Vậy \(x=\dfrac{1}{4}\)

d) \(231-\left(x-6\right)=1339:13\)

\(\Leftrightarrow231-x+6=103\)

\(\Leftrightarrow237-x=103\)

\(\Leftrightarrow237-x+6=103\)

\(\Leftrightarrow-x=103-237\)

\(\Leftrightarrow-x=-134\)

\(\Leftrightarrow x=134\)

e) đề j mà có 2 dấu bằng >> sai :v

f) \(28-x^3=1\)

\(\Leftrightarrow-x^3=1-28\)

\(\Leftrightarrow-x^3=-27\)

\(\Leftrightarrow x^3=27\)

\(\Leftrightarrow x^3=3^3\)

\(\Leftrightarrow x=3\)

Vậy \(x=3\)

g) \(\left(x+2\right)^3=27\)

\(\Leftrightarrow\left(x+2\right)^3=3^3\)

\(\Leftrightarrow x+2=3\)

\(\Leftrightarrow x=3-2\)

\(\Leftrightarrow x=1\)

Vậy \(x=1\)

h) \(81-\left(x-5\right)^2=56\)

\(\Leftrightarrow-\left(x-5\right)^2=56-81\)

\(\Leftrightarrow-\left(x-5\right)^2=-25\)

\(\Leftrightarrow\left(x-5\right)^2=25\)

\(\Leftrightarrow x-5=\pm5\)

\(\Leftrightarrow\left[{}\begin{matrix}x-5=5\\x-5=-5\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=5+5\\x=-5+5\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=10\\x=0\end{matrix}\right.\)

Vậy \(x_1=0;x_2=10\)

j) \(x^2=9\)

\(\Leftrightarrow x=\pm3\)

\(\Leftrightarrow\left[{}\begin{matrix}x=3\\x=-3\end{matrix}\right.\)

Vậy \(x_1=-3;x_2=3\)

l) tự làm.

26 tháng 6 2017

(x-12):6=3
x^2-1=3
mình nhâm

28 tháng 8 2021

a) \(x:\dfrac{6}{13}=\dfrac{13}{7}\\ \Rightarrow x=\dfrac{13}{7}.\dfrac{6}{13}\\ \Rightarrow x=\dfrac{6}{7}\)

b) \(\dfrac{4}{7}.x-\dfrac{2}{3}=\dfrac{1}{5}\\ \Rightarrow\dfrac{4}{7}.x=\dfrac{13}{15}\\ \Rightarrow x=\dfrac{91}{60}\)

c) \(\left(\dfrac{3}{10}-x\right):\dfrac{2}{5}=\dfrac{3}{5}\\ \Rightarrow\dfrac{3}{10}-x=\dfrac{6}{25}\\ \Rightarrow x=\dfrac{3}{50}\)

d) \(\dfrac{2}{3}x-\dfrac{7}{6}=\dfrac{5}{2}\\ \Rightarrow\dfrac{2}{3}x=\dfrac{11}{3}\\ \Rightarrow x=\dfrac{11}{2}\)

28 tháng 8 2021

đc!

10 tháng 7 2023

`1, -2/9 xx 15/17 + (-2/9) xx 2/17`

`= -2/9 xx (15/17 + 2/17)`

`= -2/9 xx 17/17`

`=-2/9xx1`

`=-2/9`

__

`-5/3 xx 6/5 + (-7/9) xx 3/10`

`= -30/15 + (-21/90)`

`= -2 + (-7/30)`

`=-60/30 +(-7/30)`

`=-67/30`

__

`15/20 xx 7/5 + (-9/7) xx (-6/4)`

`=3/4 xx7/5 + (-9/7) xx(-6/4)`

`= 21/20 + 54/28`

`= 21/20 + 27/14`

`=417/140`

__

`-25/13 xx 5/19 + (-25/13) xx 14/19`

`=-25/13 xx (5/19 +14/19)`

`=-25/13 xx 19/19`

`= -25/13 xx 1`

`=-25/13`

__

`-7/13 xx 13/5 + (-9/7) xx 5/3`

`=-7/5 +(-15/7)`

`=-124/35`

27 tháng 7 2023

có đúng ko