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.

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

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

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

Bạn chia từng bài ra được chứ?

Ta có: \(20\%\cdot x+\frac58x\cdot0,5=\frac{11}{26}\)

=>\(x\cdot\frac15+x\cdot\frac58\cdot\frac12=\frac{11}{26}\)

=>\(x\left(\frac15+\frac{5}{16}\right)=\frac{11}{26}\)

=>\(x\cdot\frac{41}{80}=\frac{11}{26}\)

=>\(x=\frac{11}{26}:\frac{41}{80}=\frac{11}{26}\cdot\frac{80}{41}=\frac{11\cdot40}{41\cdot13}=\frac{440}{533}\)

`1/2 : x-5/6 =-2/3`

`=> 1/2 : x=-2/3 +5/6`

`=> 1/2 : x= -4/6 +5/6`

`=> 1/2 : x=1/6`

`=>x=1/2:1/6`

`=>x= 1/2 xx 6`

`=>x= 6/2`

`=>x=3`

Vậy `x=3`

__

`20% . x +5/8 -x . 0,5 =11/20`

`=> 20/100 . x + 5/8 - x . 5/10=11/20`

`=> 1/5 . x+5/8 - x. 1/2 =11/20`

`=> (1/5 -1/2) . x+5/8=11/20`

`=>-3/10 . x+ 5/8 =11/20`

`=> -3/10 . x=11/20 -5/8`

`=>-3/10 .x=-3/40`

`=> x= -3/40 : (-3/10)`

`=> x=-3/40 xx (-10/3)`

`=>x= 1/4`

Vậy `x=1/4`

` @ ` \(\text{Nguyễn Hoàng Duy Khánh}\)

mình vừa giải câu ở dưới r nhe 

Tự làm dễ mà 

a: =>(2x+1/2)^2=1/4

=>2x+1/2=1/2 hoặc 2x+1/2=-1/2

=>x=-1/2 hoặc x=0

b: =>(x-1/5)^2=49

=>x-1/5=7 hoặc x-1/5=-7

=>x=-6,8 hoặc x=7,2

c: =>1,2x=12

=>x=10

d: =>3/4x+1/2x+1/2=-11/4

=>5/4x=-11/4-2/4=-13/4

=>x=-13/5

e: =>-0,25x+1,25x=0,2

=>x=0,2

11×[(62+(-12)]+50+11

11×51+50+11

561+50+11

611+11

622

(5/13+8/13)+(-20/41+-21/41)+-5/7

1+-1+-5/7

-5/7

bn nhân tích chéo rồi tự tính nhé

a) \(x+5=20-\left(12-7\right)\)

\(\Rightarrow x+5=20-5\)

\(\Rightarrow x+5=15\)

\(\Rightarrow x=15-5\)

\(\Rightarrow x=10\)

b) \(15-\left(3+2x\right)=2^2\)

\(\Rightarrow3+2x=15-4\)

\(\Rightarrow3+2x=11\)

\(\Rightarrow2x=11-3\)

\(\Rightarrow2x=8\)

\(\Rightarrow x=\dfrac{8}{2}\)

\(\Rightarrow x=4\)

c) \(-11-\left(19-x\right)=50\)

\(\Rightarrow19-x=-11-50\)

\(\Rightarrow19-x=-61\)

\(\Rightarrow x=61+19\)

\(\Rightarrow x=80\)

d) \(159-\left(25-x\right)=43\)

\(\Rightarrow25-x=159-43\)

\(\Rightarrow25-x=116\)

\(\Rightarrow x=25-116\)

\(\Rightarrow x=-91\)

e) \(\left(79-x\right)-43=-\left(17-52\right)\)

\(\Rightarrow\left(79-x\right)-43=52-17\)

\(\Rightarrow79-x-43=35\)

\(\Rightarrow36-x=35\)

\(\Rightarrow x=1\)

f) \(\left(7+x\right)-\left(21-13\right)=32\)

\(\Rightarrow7+x-8=32\)

\(\Rightarrow x-1=32\)

\(\Rightarrow x=32+1\)

\(\Rightarrow x=33\)

g) \(-x+20=-15+8+13\)

\(\Rightarrow-x+20=6\)

\(\Rightarrow x=20-6\)

\(\Rightarrow x=14\)

h) \(-\left(-x+13-142\right)+18=55\)

\(\Rightarrow x-13+142+18=55\)

\(\Rightarrow x+147=55\)

\(\Rightarrow x=55-147\)

\(\Rightarrow x=-92\)