x=-3

x=-3

2x-(-20)=14

2x=14+(-20)

2x=-6

x=-6:2

x=-3

***a, 14+2x=-32

        2x=-32-14

        2x=-46

          x=-46/2

         x=-23

        Vậy x=-23

ko biết ahihi

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\(\left(20x-x\right)-\left(-14-2x\right)+\left(-35-x\right)=5-3x\)

\(20-x+14+2x-35-x=5-3x\)

\(-1=5-3x\)

\(3x=5+1\)

\(3x=6\)

\(x=6:3\)

\(x=2\)

( 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

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, \(\frac{7}{2}.x-20\%.x=-4\)

\(\Rightarrow x\left(\frac{7}{2}-20\%\right)=-4\)

\(\Rightarrow x\left(\frac{7}{2}-\frac{1}{5}\right)=-4\)

\(\Rightarrow x\frac{7}{10}=-4\)

\(\Rightarrow x=-4:\frac{7}{10}\)

\(\Rightarrow x=-\frac{40}{7}\)

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

\(\Leftrightarrow\left(y-2\right)^2+10=\dfrac{20}{\left(x+1\right)^2+2}\)

Ta có: \(\left(y-2\right)^2+10\ge10\)

\(\left(x+1\right)^2+2\ge2\Rightarrow\dfrac{20}{\left(x+1\right)^2+2}\le\dfrac{20}{2}=10\)

\(\Rightarrow\left(y-2\right)^2+10\ge\dfrac{20}{\left(x+1\right)^2+2}\)

Đẳng thức xảy ra khi và chỉ khi:

\(\left\{{}\begin{matrix}y-2=0\\x+1=0\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x=-1\\y=2\end{matrix}\right.\)

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

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.

$-12-(-2)x=-2-4=-6$

$(-2)x=-12-(-6)=-12+6=-6$

$x=(-6):(-2)=3$