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6 tháng 12 2021

 

https://hoc24.vn/cau-hoi/tim-x-bieta-x-12-15-b-123-5x438.3496371618478

6 tháng 12 2021

a) x-12=-15
x=-15+12
x=-3
b) 123-5(x+4)=38
5(x+4)=123-38
5(x+4)=85
x+4=85:5=17
x=17-4
x=13

6 tháng 12 2021

\(a.x-12=-15\)                    \(b.123-5.\left(x+4\right)=38\)

\(x=\left(-15\right)+12\)                        \(5.\left(x+4\right)=123-38\)

\(x=-3\)                                      \(5.\left(x+4\right)=85\)           

                                                   \(x+4=85:5=17\)

                                                    \(x=17-4=13\)

6 tháng 3 2016

a,\(\frac{5}{8}\times0=0\)

b.\(\frac{8}{21\times1}\)=\(\frac{8}{21}\)

10 tháng 1 2022

1. \(\dfrac{-1}{7}-\dfrac{1}{8}=\dfrac{-8-7}{56}=\dfrac{-15}{56}.\)

2. \(\dfrac{15}{48}-\dfrac{5}{12}=\dfrac{5}{16}-\dfrac{5}{12}=-\dfrac{5}{48}.\)

3. \(\dfrac{-3}{15}-\left(\dfrac{-3}{25}\right)=\dfrac{-1}{5}+\dfrac{3}{25}=\dfrac{-2}{25}.\)

4. \(\dfrac{1}{15}-\dfrac{3}{5}=\dfrac{1-9}{15}=-\dfrac{8}{15}.\)

10 tháng 1 2022

1. \(\dfrac{-1}{7}-\dfrac{1}{8}=\dfrac{-8-7}{56}=-\dfrac{15}{56}.\)

2. \(\dfrac{15}{48}-\dfrac{5}{12}=\dfrac{5}{16}-\dfrac{5}{12}=-\dfrac{5}{48}.\)

3. \(\dfrac{-3}{15}-\left(-\dfrac{3}{25}\right)=\dfrac{-1}{5}+\dfrac{3}{25}=-\dfrac{2}{25}.\)

4. \(\dfrac{1}{15}-\dfrac{3}{5}=\dfrac{1-9}{15}=-\dfrac{8}{15}.\)

8 tháng 3 2023

\(a,x-\dfrac{1}{18}=\dfrac{-4}{15}\\ \Rightarrow x=\dfrac{-4}{15}+\dfrac{1}{18}\\ \Rightarrow x=\dfrac{-19}{90}\)

\(b,2x+\dfrac{3}{4}=x-\dfrac{1}{3}\\ \Leftrightarrow2x-x=-\dfrac{1}{3}-\dfrac{3}{4}\\ \Leftrightarrow x=\dfrac{-4-9}{12}\\ \Leftrightarrow x=-\dfrac{13}{12}\)

\(c,\dfrac{x-3}{5}=\dfrac{5}{x-3}\\ \Leftrightarrow\left(x-3\right)^2=25\\ \Leftrightarrow\left[{}\begin{matrix}x-3=5\\x-3=-5\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=8\\x=-2\end{matrix}\right.\)

7 tháng 1 2022

3) \(-12+2x-9+x=0\\ -21+3x=0\\ 3x=21\\ x=7\)

7 tháng 1 2022

làm mỗi câu 3:V

8 tháng 2 2023

`5`

`a, -7/21 +(1+1/3)`

`=-7/21 + ( 3/3 + 1/3)`

`=-7/21+ 4/3`

`=-7/21+ 28/21`

`= 21/21`

`=1`

`b, 2/15 + ( 5/9 + (-6)/9)`

`= 2/15 + (-1/9)`

`= 1/45`

`c, (9-1/5+3/12) +(-3/4)`

`= ( 45/5-1/5 + 3/12)+(-3/4)`

`= ( 44/5 + 3/12)+(-3/4)`

`= 9,05 +(-0,75)`

`=8,3`

`6`

`x+7/8 =13/12`

`=>x= 13/12 -7/8`

`=>x=5/24`

`-------`

`-(-6)/12 -x=9/48`

`=> 6/12 -x=9/48`

`=>x= 6/12-9/48`

`=>x=5/16`

`---------`

`x+4/6 =5/25 -(-7)/15`

`=>x+4/6 =1/5 + 7/15`

`=> x+ 4/6=10/15`

`=>x=10/15 -4/6`

`=>x=0`

`----------`

`x+4/5 = 6/20 -(-7)/3`

`=>x+4/5 = 6/20 +7/3`

`=>x+4/5 = 79/30`

`=>x=79/30 -4/5`

`=>x= 79/30-24/30`

`=>x= 55/30`

`=>x= 11/6`

8 tháng 2 2023

\(5)\)

\(A=\dfrac{-7}{21}+\left(1+\dfrac{1}{3}\right)\)

\(A=\dfrac{-7}{21}+\dfrac{4}{3}\)

\(A=\dfrac{-7}{21}+\dfrac{28}{21}\)

\(A=1\)

\(--------------\)

\(B=\dfrac{2}{15}+\left(\dfrac{5}{9}+\dfrac{-6}{9}\right)\)

\(B=\dfrac{2}{15}+\dfrac{-1}{9}\)

\(B=\dfrac{18}{135}+\dfrac{-15}{135}\)

\(B=\dfrac{1}{45}\)

\(------------\)

\(C=9-\dfrac{1}{5}+\dfrac{3}{12}+\dfrac{-3}{4}\)

\(C=\dfrac{44}{5}+\dfrac{3}{12}+\dfrac{-3}{4}\)

\(C=\dfrac{528}{60}+\dfrac{15}{60}+\dfrac{-3}{4}\)

\(C=\dfrac{181}{20}+\dfrac{-3}{4}\)

\(C=\dfrac{181}{20}+\dfrac{-15}{20}\)

\(C=\dfrac{83}{10}\)

\(6)\)

\(a)\) \(x+\dfrac{7}{8}=\dfrac{13}{12}\)

\(x=\dfrac{13}{12}-\dfrac{7}{8}\)

\(x=\dfrac{104}{96}-\dfrac{84}{96}\)

\(x=\dfrac{5}{24}\)

\(b)\) \(\dfrac{-6}{12}-x=\dfrac{9}{48}\)

\(\dfrac{-1}{2}-x=\dfrac{3}{16}\)

\(x=\dfrac{-1}{2}-\dfrac{3}{16}\)

\(x=\dfrac{-8}{16}-\dfrac{3}{16}\)

\(x=\dfrac{-11}{16}\)

\(c)\) \(x+\dfrac{4}{6}=\dfrac{5}{25}-\left(-\dfrac{7}{15}\right)\)

\(x+\dfrac{4}{6}=\dfrac{5}{25}+\dfrac{7}{15}\)

\(x+\dfrac{4}{6}=\dfrac{75}{375}+\dfrac{105}{375}\)

\(x+\dfrac{4}{6}=\dfrac{12}{25}\)

\(x=\dfrac{12}{25}-\dfrac{4}{6}\)

\(x=\dfrac{72}{150}-\dfrac{100}{150}\)

\(x=\dfrac{-14}{75}\)

\(d)\) \(x+\dfrac{4}{5}=\dfrac{6}{20}-\left(-\dfrac{7}{3}\right)\)

\(x+\dfrac{4}{5}=\dfrac{6}{20}+\dfrac{7}{3}\)

\(x+\dfrac{4}{5}=\dfrac{18}{60}+\dfrac{140}{60}\)

\(x+\dfrac{4}{5}=\dfrac{79}{30}\)

\(x=\dfrac{79}{30}-\dfrac{4}{5}\)

\(x=\dfrac{79}{30}-\dfrac{24}{30}\)

\(x=\dfrac{11}{6}\)