Bài 1: 

a) =25,97+(6,54+103,46)

=25,97+110

=135,97

b)136x75+75x64

=75x(136+64)

=75x200

=15 000

c) (21/8+1/2):5/16

=(21/8+4/8)x16/5

=25/8x16/5

=10

d)3/17-4/5+14/17

=(3/17+14/17)-4/5

=1-4/5

=1/5

Bài 2:

a)720:\([41-(2x-5)]\)=120

              41 - (2x-5)                 =720:120

              41 - (2x-5)                 =6

                      2x-5                   =41-6

                      2x-5                   =35

                      2x                      =35+5

                      2x                      =40

                      x                        =40:2

                      x                        =20

b)2/3 x X +3/4=3

   2/3 x X        =3-3/4

   2/3 x X        =12/4-3/4

   2/3 x X        =9/4

             x        =9/4:2/3

             x        =9/4x3/2

             x        =27/8

c) x+0,34=1,19x1,02

    x+0,34=1,2138

    x         =1,2138-0,34

    x         =0,8738

a: \(=\dfrac{5}{4}\cdot\dfrac{2}{5}\cdot\dfrac{17}{21}\cdot\dfrac{7}{34}=\dfrac{1}{2}\cdot\dfrac{1}{2}\cdot\dfrac{1}{3}=\dfrac{1}{12}\)

b: =>0,5^x(0,5+1)=1,5

=>0,5^x=1

=>x=0

c: =>x*0,05-0,25*x=-1,2

=>-0,3*x=-1,2

=>x=4

d: =>x-1=1 hoặc x-1=-1

=>x=0 hoặc x=2

e: =5+4=9

a) \(\dfrac{2}{3}x-\dfrac{1}{2}=\dfrac{1}{10}\)

\(\dfrac{2}{3}x=\dfrac{1}{10}+\dfrac{1}{2}=\dfrac{3}{5}\)

\(x=\dfrac{3}{5}:\dfrac{2}{3}=\dfrac{9}{10}\)

b) \(\dfrac{39}{7}:x=13\)

\(x=\dfrac{\dfrac{39}{7}}{13}=\dfrac{3}{7}\)

c) \(\left(\dfrac{14}{5}x-50\right):\dfrac{2}{3}=51\)

\(\dfrac{14}{5}x-50=51\cdot\dfrac{2}{3}=34\)

\(\dfrac{14}{5}x=34+50=84\)

\(x=\dfrac{84}{\dfrac{14}{5}}=30\)

d) \(\left(x+\dfrac{1}{2}\right)\left(\dfrac{2}{3}-2x\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x+\dfrac{1}{2}=0\\\dfrac{2}{3}-2x=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{1}{2}\\x=\dfrac{1}{3}\end{matrix}\right.\)

e) \(\dfrac{2}{3}x-\dfrac{1}{2}x=\dfrac{5}{12}\)

\(\dfrac{1}{6}x=\dfrac{5}{12}\)

\(x=\dfrac{5}{12}:\dfrac{1}{6}=\dfrac{5}{2}\)

g) \(\left(x\cdot\dfrac{44}{7}+\dfrac{3}{7}\right)\dfrac{11}{5}-\dfrac{3}{7}=-2\)

\(\left(x\cdot\dfrac{44}{7}+\dfrac{3}{7}\right)\cdot\dfrac{11}{5}=-2+\dfrac{3}{7}=-\dfrac{11}{7}\)

\(x\cdot\dfrac{44}{7}+\dfrac{3}{7}=-\dfrac{11}{7}:\dfrac{11}{5}=-\dfrac{5}{7}\)

\(\dfrac{44}{7}x=-\dfrac{5}{7}-\dfrac{3}{7}=-\dfrac{8}{7}\)

\(x=-\dfrac{8}{7}:\dfrac{44}{7}=-\dfrac{2}{11}\)

h) \(\dfrac{13}{4}x+\left(-\dfrac{7}{6}\right)x-\dfrac{5}{3}=\dfrac{5}{12}\)

\(\dfrac{25}{12}x-\dfrac{5}{3}=\dfrac{5}{12}\)

\(\dfrac{25}{12}x=\dfrac{5}{12}+\dfrac{5}{3}=\dfrac{25}{12}\)

\(x=1\)

Mỏi tay woa bn làm nốt nha!!

a: \(=\dfrac{15}{4}:\dfrac{2-7}{16}-\dfrac{5}{9}\cdot\left(\dfrac{3}{5}+\dfrac{4}{5}\right)\)

\(=\dfrac{15}{4}\cdot\dfrac{16}{-5}-\dfrac{5}{9}\cdot\dfrac{7}{5}\)

\(=\dfrac{-240}{20}-\dfrac{7}{9}=-12-\dfrac{7}{9}=\dfrac{-115}{9}\)

c: \(=\dfrac{1}{5}-\dfrac{7}{2}-\dfrac{3}{2}+\dfrac{5}{4}\)

\(=\dfrac{4+25}{20}-5=\dfrac{29}{20}-\dfrac{100}{20}=\dfrac{-71}{20}\)

d: \(=\dfrac{12}{17}\left(1-\dfrac{1}{15}-\dfrac{4}{5}+1\right)=\dfrac{12}{17}\cdot\dfrac{17}{15}=\dfrac{12}{15}=\dfrac{4}{5}\)

e: \(=\dfrac{2}{15}\cdot\dfrac{9}{8}-\dfrac{7}{4}\cdot\dfrac{9}{8}+\dfrac{25}{36}\)

\(=\dfrac{9}{8}\left(\dfrac{2}{15}-\dfrac{7}{4}\right)+\dfrac{25}{36}\)

\(=\dfrac{9}{8}\cdot\dfrac{8-105}{60}+\dfrac{25}{36}\)

\(=\dfrac{9}{8}\cdot\dfrac{-97}{60}+\dfrac{25}{36}=\dfrac{-1619}{1440}\)

a) 3+2*x=15

2x=15-3

2x=12

x=12:2

x=6

Vậy x=6

b) 24-x=19

x=24-19

x=5

Vậy x=5

c) 29x-13=45

29x=45+13

29x=58

x=58:29

x=2

Vậy x=2

d) 5x-17=38

5x=38+17

5x=55

x=55:5

x=11

Vậy x=11

e) 50-2(x+1)=20

2(x+1)=50-20

2(x+1)=30

x+1+30/2

x+1=15

x=15-1=14

Vậy x=14

f) 

a)-7129+1478+7129+(-1429)
=(-7129+7129)+(1478-1429)
=0+(-1)
=-1

b)\(|-5|.\left(-7\right)+4.\left(-9\right) \)
=5.(-7)+(-36)
=-35+(-36)
=-71

c)\(|-15+21|-|4-11|\)
=\(|6|-|-7|\)
=\(6-7\)
=-1

d)1-2+3-4+5-6+...+2009-2010+2011
xét dãy số có:
số số hạng là: (2011-1):1+1=2011(số hạng)
vì 2011:2=1005(dư 1) nên ta nhóm như sau:
=(1-2)+(3-4)+(5-6)+...+(2009-2010)+2011
=-1.1005+2011
=-1005+2011
=1006

e)5+(-8).3
=5+(-24)
=-19

f)4+(-5).2
=4+(-10)
=-6

h)40-(-7).2
=40-(-14)
=40+14
=54

k)1-2-3+4+5-6-7+8+...+801-802-803+804
Xét dãy số có:
số số hạng là: (804-1):1+1=804(số hạng)
vì 804:4=201 nên ta nhóm như sau:
=(1-2-3+4)+(5-6-7+8)+...(801-802-803+804)
=0+0+...+0
=0

bài 2:
a)x+5=-2+11
x+5=9
x=9-5
x=4
vậy...

b)-3x=-5+29
-3x=24
x=24:(-3)
x=-8
vậy...

c)\(|x|-9=-2+17\)
\(|x|-9=15 \)
\(|x|=15+9\)
\(|x|=24\)
\(\Rightarrow\left\{{}\begin{matrix}x=24\\x=-24\end{matrix}\right.\)
Vậy x\(\in\)\(\left\{24;-24\right\}\)

d)\(|x-9|=-2+17\)
\(|x-9|=15\)
\(\Rightarrow\left\{{}\begin{matrix}x-9=15\\x-9=-15\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}x=15+9\\x=-15+9\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}x=24\\x=-6\end{matrix}\right.\)
Vậy x\(\in\left\{24;-6\right\}\)

e)x-2=-6+17
x-2=11
x=11+2
x=13
vậy...

f)x+2=-9-11
x+2=-20
x=-20-2
x=-24
vậy...

g)2x+5=x-1
2x-x=-1-5
x=-6
vậy...

h)\(|x-4|=|-81|\)
\(|x-4|=81\)
\(\Rightarrow\left\{{}\begin{matrix}x-4=81\\x-4=-81\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}x=81+4\\x=-81+4\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}x=85\\x=-77\end{matrix}\right.\)
vậy \(x\in\left\{85;-77\right\}\)

k)x+9=2-17
x+9=-15
x=-15-9
x=-24
vậy...

m)x-17=(-11).(-5)
x-17=55
x=55-17
x=38
vậy...

n)\(|x-5|=\left(-4\right).2 \)
\(|x-5|=-8\) (loại)
vậy \(x\in\left\{\varnothing\right\}\)

Bài 1. Tính:
a) -7129 + 1478 + 7129 + (-1479)

= -7129 + 7129 + 1478 + ( -1479 )

= 0 + (-1) = -1

b) | -5 | . (-7) + 4 . (-9)

= 5 . (-7) + (-36)

= (-35) + (-36) = -71

c) | -15 + 21| – | 4 – 11|

= | 6 | - | -7| = 6 - 7 = -1
e) 5 + (-8).3

= 5 + (-24) = -19

f) 4 + (-5)2

= 4 + (-10) = -6

g) 49 + (11 – 25)

= 49 + (-14) = 35

h) 40 – (-7)2

= 40 - (-14) = 54
Bài 2. Tìm x ∈ Z, biết:
a) x + 5 = -2 + 11

x + 5 = 9

x = 9 - 5

x = 4

Vậy x = 4

b) -3x = -5 + 29

-3x = 24

x = 24 : (-3)

x = -8

Vậy x = -8

c) | x | - 9 = -2 + 17

| x | - 9 = 15

| x | = 15 + 9

| x | = 24

=> [\(\begin{matrix} x=24 \\ x=-24 \end{matrix}\)

Vậy..

d) | x – 9 | = -2 + 17

| x - 9 | = 15

=>[ \(\begin{matrix} x-9=15<=>x=24\\ x-9=-15<=>x=-6 \end{matrix}\)

Vậy..
e) x – 2 = -6 + 17

x - 2 = 11

x = 11 + 2

x = 13

Vậy x =13

f) x + 2 = -9 – 11

x + 2 = -20

x = -20-2

x = -22

Vậy x =-22

g) 2x + 5 = x – 1

2x - x = -1 -5

x = -6

Vậy x = -6

h) |x – 4| = | -81 |

| x - 4 | = 81

=>[\(\begin{matrix} x-4=81<=>x=85\\ x-4=-81<=>x =-85 \end{matrix}\)

Vậy..
k) x + 9 = 2 – 17

x + 9 = -15

x = -15 - 9

x = -24

Vậy x = -24

m) x - 17 = (-11) . (-5)

x - 17 = 55

x = 55 + 17

x = 72

Vậy x = 72

Bài 1:
a)=(-7129+7129)+(1478-1479)
=0+(-1)
=-1

b)=5.(-7)+(-36)
=-35-36
=-71

c)=\(|6|-|-3|\)
=6-3
=3

d)Xét dãy số có:
Số số hạng là: (2011-1):1+1=2011(số hạng)
Vì 2011:2=1005(dư 1) nên ta nhóm như sau:
=(1-2)+(3-4)+(5-6)+...+(2007-2008)+(2009-2010)+2011
=-1+(-1)+(-1)+...+(-1)+(-1)+2011
=-1.1005+2011
=-1005+2011
=1006

e)=5+(-24)
=5-24
=-19

f)=4+(-10)
=4-10
=-6

g)=49+(-14)
=49-14
=35

k)Xét dãy số có:
Số số hạng là: (804-1):1+1=804(số hạng)
Vì 804:4=201 nên ta nhóm như sau:
=(1-2-3+4)+(5-6-7+8)+...+(801-802-803+804)
=0+0+...+0
=0

đây bạn

a) \(\dfrac{x}{5}+\dfrac{1}{2}=\dfrac{6}{10}\\ \dfrac{x}{5}+\dfrac{1}{2}=\dfrac{3}{5}\\ \dfrac{x}{5}=\dfrac{3}{5}-\dfrac{1}{2}\\ \dfrac{x}{5}=\dfrac{6}{10}-\dfrac{5}{10}\\ \dfrac{x}{5}=\dfrac{1}{10}\\ \dfrac{2x}{10}=\dfrac{1}{10}\\ \Rightarrow2x=1\\ x=1:2\\ x=0,5=\dfrac{1}{2}\)

b) \(x+\dfrac{3}{15}=\dfrac{1}{3}\\ x=\dfrac{1}{3}-\dfrac{3}{15}\\ x=\dfrac{5}{15}-\dfrac{3}{15}\\ x=\dfrac{2}{15}\)

c) \(x-\dfrac{12}{4}=\dfrac{1}{2}\\ x-3=\dfrac{1}{2}\\ x=\dfrac{1}{2}+3\\ x=\dfrac{1}{2}+\dfrac{6}{2}\\ x=\dfrac{7}{2}\)

d) \(\dfrac{1}{2}x+\dfrac{1}{2}=\dfrac{5}{2}\\ \dfrac{1}{2}x=\dfrac{5}{2}-\dfrac{1}{2}\\ \dfrac{1}{2}x=2\\ x=2:\dfrac{1}{2}\\ x=4\)

a. \(\dfrac{2x+5}{10}=\dfrac{6}{10}\Leftrightarrow2x=1\Leftrightarrow x=\dfrac{1}{2}\)

b. \(\dfrac{15x+3}{15}=\dfrac{5}{15}\Leftrightarrow15x=2\Leftrightarrow x=\dfrac{2}{15}\)

c. \(\dfrac{4x-12}{4}=\dfrac{2}{4}\Leftrightarrow4x=14\Leftrightarrow x=\dfrac{7}{2}\)

d. \(\dfrac{1+x}{2x}=\dfrac{5x}{2x}\Leftrightarrow-4x=-1\Leftrightarrow x=\dfrac{1}{4}\)

e. \(\dfrac{-4\left(2x-5\right)}{6\left(2x-5\right)}-\dfrac{2}{6\left(2x-5\right)}=\dfrac{9\left(2x-5\right)}{6\left(2x-5\right)}\)

\(\Leftrightarrow-8x+20-2=18x-45\)

\(\Leftrightarrow-26x=-63\Leftrightarrow x=\dfrac{63}{26}\)

f. \(\left(3x-1\right)\left(\dfrac{-1}{2x+5}\right)=0\)

\(\left[{}\begin{matrix}3x-1=0\Rightarrow3x=1\Rightarrow x=\dfrac{1}{3}\\\dfrac{-1}{2x+5}=0\Rightarrow2x+5=0\Rightarrow2x=-5\Rightarrow x=\dfrac{-5}{2}\end{matrix}\right.\)

g. \(\dfrac{6x}{12x}-\dfrac{8}{12x}=\dfrac{7x}{12x}\Leftrightarrow-x=8\Leftrightarrow x=-8\)

h. \(\dfrac{45}{60x}+\dfrac{12x}{6x}=\dfrac{10x}{60x}\Leftrightarrow2x=-45\Leftrightarrow x=\dfrac{-45}{2}\)

một đòn bẫy dài một mét .đặt ở đâu để có thể dùng 3600n có thể nâng tảng đá nặng 120kg?