2x - (-20)=14
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2x - (-20) = 14
2x = 14 + (-20)
2x = -6
x =-6:2
x = -3
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\left(20x-x\right)-\left(-14-2x\right)+\left(-35-x\right)=5-3x\)
\(20-x+14+2x-35-x=5-3x\)
\(-1=5-3x\)
\(3x=5+1\)
\(3x=6\)
\(x=6:3\)
\(x=2\)
( 20 - x ) - ( -14 - 2x ) + ( -35 - x ) = 5 - 3x
20 - x + 14 + 2x - 35 - x =5-3x
20 - x + 14 + 2x - 35 - x + 3x =5
( -x + 2x - x + 3x ) + ( 20 + 14 - 35 ) = 5
3x - 1 = 5
3x = 5 + 1
3x = 6
x = 6 : 3
x = 2
Vậy x = 2
![](https://rs.olm.vn/images/avt/0.png?1311)
a,\(\left(\frac{7}{5}-2x\right).\frac{40}{20}=\frac{8}{14}\)
\(\Rightarrow\left(\frac{7}{5}-2x\right).2=\frac{4}{7}\)
\(\Rightarrow\frac{7}{5}-2x=\frac{4}{7}:2\)
\(\Rightarrow\frac{7}{5}-2x=\frac{2}{7}\)
\(\Rightarrow2x=\frac{7}{5}-\frac{2}{7}\)
\(\Rightarrow2x=\frac{39}{35}\)
\(\Rightarrow x=\frac{39}{35}:2\)
\(\Rightarrow x=\frac{39}{70}\)
b, \(\frac{7}{2}.x-20\%.x=-4\)
\(\Rightarrow x\left(\frac{7}{2}-20\%\right)=-4\)
\(\Rightarrow x\left(\frac{7}{2}-\frac{1}{5}\right)=-4\)
\(\Rightarrow x\frac{7}{10}=-4\)
\(\Rightarrow x=-4:\frac{7}{10}\)
\(\Rightarrow x=-\frac{40}{7}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
gợi ý:
sử dụng \(\left|x\right|=a\Leftrightarrow x=a\) hoặc \(x=-a\)
bài1 : TH1 x^2-2x-1=14
=> x^2-2x+1=16
=>(x-1)^2=16
=>x=5 hoặc -3
TH2 x^2-2x-1=-14
=>(x-1)^2=-12(vô lí)
baif2:làm tương tự như bài 1
![](https://rs.olm.vn/images/avt/0.png?1311)
a: =>x/27+1=-2/3
=>x/27=-5/3
=>x=-45
b: \(\Leftrightarrow x-4=\dfrac{2}{5}:\dfrac{20}{21}=\dfrac{2}{5}\cdot\dfrac{21}{20}=\dfrac{42}{100}=\dfrac{21}{50}\)
=>x=221/50
c: \(\Leftrightarrow x+\dfrac{2}{3}=\dfrac{4}{60}=\dfrac{1}{15}\)
=>x=1/15-2/3=1/15-10/15=-9/15=-3/5
d: \(\Leftrightarrow x\cdot\dfrac{3}{5}=\dfrac{1}{5}-\dfrac{15}{14}\cdot\dfrac{21}{20}\)
=>\(x\cdot\dfrac{3}{5}=\dfrac{1}{5}-\dfrac{3}{2}\cdot\dfrac{3}{4}=\dfrac{1}{5}-\dfrac{9}{8}=\dfrac{-37}{40}\)
=>x=-37/24
e: =>-3/7x=84/45
=>x=-196/45
f: =>11/10x=-2/3
=>x=-20/33
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1:
a. $(-20)+x=-30$
$x-20=-30$
$x=-30+20=-(30-20)=-10$
b.
$(-10)-x=-20$
$x=(-10)-(-20)=-10+20=20-10=10$
c. Đề sai. Bạn xem lại.
d.
$x+(-3)=-7$
$x=-7-(-3)=-7+3=-(7-3)=-4$
e.
$x-(-5)=-9$
$x=(-9)+(-5)=-14$
f.
$x(-11)=12$
$x=\frac{12}{-11}=\frac{-12}{11}$
h.
$2x-10=20$
$2x=20+10=30$
$x=30:2=15$
l.
$4x-8=-8$
$4x=-8+8=0$
$x=0:4=0$
k.
$-12-(-2)x=-8$
$(-2)x=-12-(-8)=-12+8=-(12-8)=-4$
$x=(-4):(-2)=2$
Bài 2:
a. $-20-(10-x)=-3$
$10-x=-20-(-3)=-20+3=-(20-3)=-17$
$x=10-(-17)=10+17=27$
b.
$14+(14-x)=-2$
$14-x=-2-14=-16$
$x=14-(-16)=14+16=30$
c.
$-15-(x-3)=-7$
$x-3=-15-(-7)=-15+7=-8$
x=-8+3=-5$
d.
$(x+4)+(-20)=-8$
$x+4=-8-(-20)=-8+20=12$
$x=12-4=8$
e.
$-2x-2=-4$
$-2x=-4+2=-2$
$x=(-2):(-2)=1$
f.
$-2x+4=-4$
$-2x=-4-4=-8$
$x=(-8):(-2)=4$
l.
$-12-(-2)x=-2-4=-6$
$(-2)x=-12-(-6)=-12+6=-6$
$x=(-6):(-2)=3$
x=-3
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