Câu 1

a)(-9)+(-3) = -9 - 3 = -12

b)6.7.5²+42.75 = 42. 25 + 42. 75 = 42(25 + 75) = 42. 100 = 4200

c)4529-(186+4529) = 4529 - 186 - 4529 = -186

Câu 2

a)x-7=15

<=> x = 15 + 7

<=> x = 22

b)9+4.(x-5)=17

<=> 9 + 4x - 20 = 17

<=> 4x = 28

<=> x = 7

c)(x-3)³=27

<=> (x - 3)³ = 3³

=> x - 3 = 3

<=> x = 6

Câu 1: 

a) Ta có: (-9)+(-3)

=-(9+3)

=-12

b) Ta có: \(6\cdot7\cdot5^2+42\cdot75\)

\(=6\cdot7\cdot5^2+6\cdot7\cdot5^2\cdot3\)

\(=6\cdot7\cdot5^2\cdot\left(1+3\right)\)

\(=6\cdot7\cdot25\cdot4\)

\(=42\cdot100=4200\)

c) Ta có: 4529-(186+4529)

=4529-186-4529

=-186

Câu 2: 

a) Ta có: x-7=15

\(\Leftrightarrow x=15+7\)

hay x=22

Vậy: x=22

b) Ta có: \(9+4\left(x-5\right)=17\)

\(\Leftrightarrow9+4x-20=17\)

\(\Leftrightarrow4x-11=17\)

\(\Leftrightarrow4x=28\)

hay x=7

Vậy: x=7

c) Ta có: \(\left(x-3\right)^3=27\)

\(\Leftrightarrow\left(x-3\right)^3=3^3\)

\(\Leftrightarrow x-3=3\)

hay x=6

Vậy: x=6

186-3(x+7)=6

3(x+7)=186-6

3(x+7)=180

x+7=180:3

x+7=60

x=60-7

x=53

Vay x=53

a) (x - 1) + (x + 2) + (x - 3) + (x + 4) + (x - 5) + (x + 6) = 21

x - 1 + x + 2 + x - 3 + x + 4 + x - 5 + x + 6 = 21

6x + 3 = 21

6x = 21 - 3

6x = 18

x = 18 : 6 

x = 3

b) (x - 1) + (x + 3) + (x - 5) + (x + 7) + (x - 9) + (x + 11) = 186

x - 1 + x + 3 + x - 5 + x + 7 + x - 9 + x + 11 = 186

6x + 6 = 186

6x = 186 - 6

6x = 180

x = 180 : 6

x = 30

5) - 12 + 3(-x + 7) = -18

              3(-x+7) = -18- -12

              3(-x+7) = -30

                 -x+7 = -30 : 3

                  -x+7 = -10

                   -x    = -10 -7 = -17 

     Vậy x= 17

                   
6) 24 : (3x – 2) = -3

          ( 3x - 2)  = 24: -3 

          3x - 2 = -8 

           3x      = -8 +2

           3x      = -6 

              x     = -6:3 = -2 

Vậy x= -2
7) -45 : 5.(-3 – 2x) = 3  

             5(-3-2x) = -45: 3

              5( -3-2x) = -15 

                -3-2x      = -15 :5 

                  -3- 2x    = -3

                       2x     = -3--3

                         2x= 0

Vậy  x= 0

\(\frac{x}{3}=\frac{y}{4}\Leftrightarrow\frac{y}{20}=\frac{x}{15};\frac{x}{5}=\frac{z}{7}\Leftrightarrow\frac{x}{15}=\frac{z}{21}\)

\(\Rightarrow\frac{x}{15}=\frac{y}{20}=\frac{z}{21}\)

Áp dụng tc dãy tỉ:

\(\frac{x}{15}=\frac{y}{20}=\frac{z}{21}\Leftrightarrow\frac{2x}{30}=\frac{3y}{60}=\frac{z}{21}=\frac{2x+3y-z}{30+60-21}=\frac{186}{69}\) lẻ đây, đề k sai thì tự lm tiếp

sai đề à

tính 2x+3y-z ra 186/69 -->lẻ

a) \(4x=3y<=>\frac{x}{3}=\frac{y}{4}=>\frac{x}{15}=\frac{y}{20}\)

\(7y=5z<=>\frac{y}{5}=\frac{z}{7}=>\frac{y}{20}=\frac{z}{28}\)

Ap dung tinh chat bac cau ta duoc:

\(\frac{x}{15}=\frac{y}{20}=\frac{z}{28}=>\frac{2x}{30}=\frac{3y}{60}=\frac{z}{28}=\frac{2x+3y-z}{30+60-28}=\frac{186}{62}=3\)

=> x = 45  ;  y=60  ;  z=84

Answer:

1.

\(\frac{x}{3}=\frac{y}{4}\Rightarrow\frac{x}{15}=\frac{y}{20}\)

\(\frac{y}{5}=\frac{z}{7}\Rightarrow\frac{y}{20}=\frac{z}{28}\)

\(\Rightarrow\frac{x}{15}=\frac{y}{20}=\frac{z}{28}\)

\(\Rightarrow2\frac{x}{30}=3\frac{y}{60}=\frac{z}{28}\)

Áp dụng tính chất của dãy tỷ số bằng nhau

\(2\frac{x}{30}+3\frac{y}{60}+\frac{z}{28}=\frac{2x+3y-z}{30+60-28}=3\)

\(\Rightarrow2\frac{x}{30}=3\Rightarrow x=45\)

\(\Rightarrow3\frac{y}{60}=3\Rightarrow y=60\)

\(\Rightarrow\frac{z}{28}=3\Rightarrow z=84\)

2.

Ta đặt: \(\frac{x}{2}=\frac{y}{3}=\frac{z}{4}=k\)

\(\Rightarrow x=2k\)

\(\Rightarrow y=3k\)

\(\Rightarrow z=4k\)

\(\Rightarrow xyz=2k.3k.4k=24.k^3=648\)

\(\Rightarrow k^3=27\Rightarrow k=3\)

\(\Rightarrow\frac{x}{2}=3\Rightarrow x=6\)

\(\Rightarrow\frac{y}{3}=3\Rightarrow y=9\)

\(\Rightarrow\frac{z}{4}=3\Rightarrow z=12\)

3.

\(3x=2y\Rightarrow\frac{x}{2}=\frac{y}{3}\)

\(4x=2z\Rightarrow\frac{x}{2}=\frac{z}{4}\)

\(\Rightarrow\frac{x}{2}=\frac{y}{3}=\frac{z}{4}\) và \(x+y+z=27\)

Áp dụng tính chất dãy tỉ số bằng nhau

\(\frac{x}{2}=\frac{y}{3}=\frac{z}{4}=\frac{x+y+z}{2+3+4}=3\)

\(\Rightarrow\frac{x}{2}=3\Rightarrow x=6\)

\(\Rightarrow\frac{y}{3}=3\Rightarrow y=9\)

\(\Rightarrow\frac{z}{4}=3\Rightarrow z=12\)