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NL
18 tháng 11 2019
A. 2.\(|3x+1|\)=\(\frac{3}{4}\)-\(\frac{5}{8}\)
2.\(|3x+1|\)=1/8
\(|3x+1|\)=1/8:2
\(|3x+1|\)=1/16
TH1 : 3x+1=1/16
3x=1/16-1
3x=-15/16
x=-15/16:3
x=-5/16
YN
18 tháng 11 2019
a,\(\frac{3}{4}-2.\left|3x+1\right|=\frac{5}{8}\)
\(\Rightarrow2.\left|3x+1\right|=\frac{3}{4}-\frac{5}{8}=\frac{6}{8}-\frac{5}{8}=\frac{1}{8}\)
\(\Rightarrow\left|3x+1\right|=\frac{1}{8}.\frac{1}{2}=\frac{1}{16}\)
\(\Rightarrow\orbr{\begin{cases}3x+1=\frac{1}{16}\\3x+1=\frac{-1}{16}\end{cases}}\)\(\Rightarrow\orbr{\begin{cases}3x=\frac{1}{16}-1=\frac{-15}{16}\\3x=\frac{-1}{16}-1=\frac{-17}{16}\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=\frac{-15}{16}.\frac{1}{3}=\frac{-5}{16}\\x=\frac{-17}{16}.\frac{1}{3}=\frac{-17}{48}\end{cases}}\)
Vậy....
b,\(\left|3x+2\right|-\left|x-3\right|=\frac{7}{2}\left(1\right)\)
Ta có bảng xét dấu
| x | \(\frac{-2}{3}\) 3 |
| 3x+2 | - 0 + | + |
| x-3 | - | - 0 + |
Nếu x<\(\frac{-2}{3}\) thì \(\left|3x+2\right|-\left|x-3\right|\) \(=-3x-2-3+x\)
\(=-2x-5\)
Từ (1) \(\Rightarrow-2x-5=\frac{7}{2}\)
\(\Rightarrow-2x=\frac{7}{2}+5=\frac{17}{2}\)
\(\Rightarrow x=\frac{17}{2}\cdot\frac{-1}{2}=\frac{-17}{4}\)(thỏa mãn x<\(\frac{-2}{3}\)
Nếu \(\frac{-2}{3}\le x\le3\)thì \(\left|3x+2\right|-\left|x-3\right|=3x+2-\left(3-x\right)\)
\(=3x+2-3+x\)
\(=2x-1\)
Từ (1)\(\Rightarrow\)\(2x-1=\frac{7}{2}\)
\(\Rightarrow2x=\frac{9}{2}\)
\(\Rightarrow x=\frac{9}{4}\)(thỏa mãn......
Còn trưonwfg hợp cuối bạn tự làm nốt nhé
23 tháng 1
a: \(\dfrac{x}{6}=\dfrac{8}{3}\)
=>\(x=6\cdot\dfrac{8}{3}=\dfrac{6}{3}\cdot8=8\cdot2=16\)
b: \(\dfrac{5}{x}=\dfrac{4}{9}\)
=>\(x=\dfrac{5\cdot9}{4}=\dfrac{45}{4}\)
c: \(\dfrac{x+3}{-4}=\dfrac{5}{20}\)
=>\(x+3=\dfrac{-4\cdot5}{20}=-1\)
=>x=-1-3=-4
d: \(\dfrac{7}{3+4x}=\dfrac{-2}{9}\)
=>\(4x+3=\dfrac{9\cdot7}{-2}=-\dfrac{63}{2}\)
=>\(4x=-\dfrac{63}{2}-3=-\dfrac{69}{2}\)
=>\(x=-\dfrac{69}{8}\)
f: ĐKXĐ: x<>1
\(\dfrac{3}{x-1}=\dfrac{x-1}{27}\)
=>\(\left(x-1\right)^2=3\cdot27=81\)
=>\(\left[{}\begin{matrix}x-1=9\\x-1=-9\end{matrix}\right.\)
=>\(\left[{}\begin{matrix}x=10\left(nhận\right)\\x=-8\left(nhận\right)\end{matrix}\right.\)
AH
14 tháng 10 2016
a, ( 44 - x ) / 3 = ( x - 12 ) / 5
=> 5 ( 44 - x ) = 3 ( x - 12 )
220 - 5x = 3x - 36
- 5x - 3x = - 36 - 220
- 8 x = - 256
x = 32
b , ( 3 - x ) / 4 = ( 2x + 7 ) / 5
=> 5 ( 3 - x ) = 4 ( 2x + 7 )
15 - 5x = 8 x + 28
- 5 x - 8 x = 28 - 15
- 13 x = 13
x = -1
KH
14 tháng 10 2016
a, \(\frac{\left(44-x\right)}{3}=\frac{\left(x-12\right)}{5}\)
=> (44 - x) . 5 = (x - 12) . 3
=> 44 - x . 5 = x - 12 .3
=> 44 - x . 5 = x - 36
=> x5 + x = - 36 - 44
=> x5 + x = - 80
=> x . (5 + 1) = - 80
=> x . 6 = - 80
=> x = - 80 : 6
=> x = - 13,3
b, \(\frac{\left(3-x\right)}{4}=\frac{\left(2x+7\right)}{5}\)
=> (3 - x) . 5 = (2x + 7) . 4
=> 3 - x . 5 = 2x + 7 . 4
=> 3 - x . 5 = 2x + 28
=> -x . 5 + 2x = 28 - 3
=> -x . 5 + 2x = 25
=> x . 5 + 2x = 25
=> x . (5 + 2) = 25
=> x . 7 = 25
=> x = 25 : 7
=> x = 3,57
XO
6 tháng 8 2020
Ta có :\(\left(\frac{3}{2}-\frac{5}{11}-\frac{3}{13}\right).\left(2x-2\right)=\left(-\frac{3}{4}+\frac{5}{22}+\frac{3}{26}\right)\)
=> \(\left(\frac{3}{2}-\frac{5}{11}-\frac{3}{13}\right).\left(2x-2\right)=-\frac{1}{2}\left(\frac{3}{2}-\frac{5}{11}-\frac{3}{13}\right)\)
=> \(2x-2=-\frac{1}{2}\)
=> \(2x=\frac{3}{2}\)
=> \(x=\frac{3}{4}\)
TN
4 tháng 10 2017
a) 1/7 - 3/5x = 3/5
3/5x= 1/7 - 3/5
3/5x = -16/35
x= -16/35 : 3/5 = -16/21
b) 3/7 - 1/2x = 5/3
1/2x = 3/7 - 5/3 = -26/21
x= -26/21 : 1/2 = -52/21
3 tháng 7 2021
a) Ta có: \(\dfrac{2x}{3}=\dfrac{3y}{4}=\dfrac{4z}{5}\)
nên \(\dfrac{x}{\dfrac{3}{2}}=\dfrac{y}{\dfrac{4}{3}}=\dfrac{z}{\dfrac{5}{4}}\)
Áp dụng tính chất của dãy tỉ số bằng nhau, ta được:
\(\dfrac{x}{\dfrac{3}{2}}=\dfrac{y}{\dfrac{4}{3}}=\dfrac{z}{\dfrac{5}{4}}=\dfrac{x+y+z}{\dfrac{3}{2}+\dfrac{4}{3}+\dfrac{5}{4}}=\dfrac{49}{\dfrac{49}{12}}=12\)
Do đó:
\(\left\{{}\begin{matrix}\dfrac{2x}{3}=12\\\dfrac{3y}{4}=12\\\dfrac{4z}{5}=12\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2x=36\\3y=48\\4z=60\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=18\\y=16\\z=20\end{matrix}\right.\)
Vậy: (x,y,z)=(18;16;20)
b) Đặt \(\dfrac{x}{5}=\dfrac{y}{3}=k\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=5k\\y=3k\end{matrix}\right.\)
Ta có: \(x^2-y^2=4\)
\(\Leftrightarrow\left(5k\right)^2-\left(3k\right)^2=4\)
\(\Leftrightarrow16k^2=4\)
\(\Leftrightarrow k\in\left\{\dfrac{1}{2};-\dfrac{1}{2}\right\}\)
Trường hợp 1: \(k=\dfrac{1}{2}\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=5k=5\cdot\dfrac{1}{2}=\dfrac{5}{2}\\y=3k=3\cdot\dfrac{1}{2}=\dfrac{3}{2}\end{matrix}\right.\)
Trường hợp 2: \(k=-\dfrac{1}{2}\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=5k=5\cdot\dfrac{-1}{2}=\dfrac{-5}{2}\\y=3k=3\cdot\dfrac{-1}{2}=\dfrac{-3}{2}\end{matrix}\right.\)
Vậy: \(\left(x,y\right)\in\left\{\left(\dfrac{5}{2};\dfrac{3}{2}\right);\left(-\dfrac{5}{2};-\dfrac{3}{2}\right)\right\}\)
H
3 tháng 7 2021
a)
Theo tính chất của dãy tỉ số bằng nhau, ta có :
\(\dfrac{x}{\dfrac{3}{2}}=\dfrac{y}{\dfrac{4}{3}}=\dfrac{z}{\dfrac{5}{4}}=\dfrac{x+y+z}{\dfrac{3}{2}+\dfrac{4}{3}+\dfrac{5}{4}}=\dfrac{49}{\dfrac{49}{12}}=12\)
Suy ra :
\(x=\dfrac{12.3}{2}=18\\ y=\dfrac{12.4}{3}=16\\ z=\dfrac{12.5}{4}=15\)
b)
\(x=\dfrac{y}{3}.5=\dfrac{5y}{3}\\ x^2-y^2=4\\ \Leftrightarrow\left(\dfrac{5y}{3}\right)^2-y^2=4\\ \Leftrightarrow\dfrac{16y^2}{9}=4\Leftrightarrow y=\pm\dfrac{3}{2} \)
Với $y = \dfrac{3}{2}$ thì $x = \dfrac{5}{2}$
Với $y = \dfrac{-3}{2}$ thì $x = \dfrac{-5}{2}$
c)
\(\dfrac{x}{y+z+1}=\dfrac{y}{z+x+1}=\dfrac{z}{x+y-2}=\dfrac{x+y+z}{2x+2y+2z}=\dfrac{1}{2}\)
Suy ra :
\(2x=y+z+1\Leftrightarrow y+z=2x-1\)
Mặt khác :
\(x+y+z=\dfrac{1}{2}\Leftrightarrow x+2x-1=\dfrac{1}{2}\Leftrightarrow x=\dfrac{1}{2}\)
\(2y=x+z+1=z+\dfrac{3}{2}\)
Mà \(y+z=0\Leftrightarrow z=-y\)
nên suy ra: \(y=\dfrac{1}{2};z=-\dfrac{1}{2}\)
\(\left(\frac{1}{7}x-\frac{2}{7}\right)\left(\frac{1}{5}x+\frac{3}{5}\right)\left(\frac{1}{3}x+\frac{4}{3}\right)=0\)
<=> \(\frac{x-2}{7}.\frac{x+3}{5}.\frac{x+4}{3}=0\)
<=> \(\frac{x-2}{7}=0\)hoặc \(\frac{x+3}{5}=0\); \(\frac{x+4}{3}=0\)
Nếu \(\frac{x-2}{7}=0\)<=> \(x-2=0\)<=> \(x=2\)
Nếu \(\frac{x+3}{5}=0\)<=> \(x+3=0\) <=> \(x=3\)
Nếu \(\frac{x+4}{3}=0\)<=> \(x+4=0\)<=> \(x=4\)
Vây x= 2 hoặc 3; 4