(7x - 15).8 - 21 = 27

(7x - 15).8 = 27 + 21

(7x - 15).8 = 48

7x - 15 = 48:8

7x - 15 = 6

7x = 6 + 15

7x = 21

x = 21 : 7

x = 3

Vậy x = 3

(7x - 15).8 - 21 = 27

(7x - 15).8 = 27 + 21

(7x - 15).8 = 48

7x - 15 = 48:8

7x - 15 = 6

7x = 6 + 15

7x = 21

x = 21 : 7

x = 3

Vậy x = 3

a: =>(7x-15)x8=48

=>7x-15=6

=>7x=21

hay x=3

\(\left(7x-15\right)8=27+21\\ \left(7x-15\right)8=48\\ 7x-15=48:8\\ 7x-15=6\\ 7x=6+15\\ 7x=21\\ x=21:7\\ x=3\)

\(\left(7x-15\right).8-21=27\\ \Rightarrow\left(7x-15\right).8=48\\ \Rightarrow7x-15=6\\ \Rightarrow7x=21\\ \Rightarrow x=3\)

a, 100 - 7 x ( x - 5 ) = 58

7 x ( x - 5 ) = 100 - 58

7 x ( x - 5 ) = 42

( x - 5 ) = 42 : 7

x - 5 = 6

x = 6 + 5

x = 11

b, 24 + 5 * x = 49

5 * x = 49 - 24

5 * x = 25

x = 25 : 5

x = 5

c, x - 105 : 21 = 15

x - 5 = 15

x = 15 + 5

x = 20

d, ( x - 105 ) : 21 = 15

( x - 105 ) = 15 x 21

x - 105 = 315

x = 315 + 105

x = 420

3. tìm số tự nhiên x biết 

a 100 - 7x [ x - 5] = 58

b 24+5 nhân x = 49

c x- 105 : 21 = 15

d { x- 105] : 21 =15

a, 100 - 7 x ( x - 5 ) = 58

7 x ( x - 5 ) = 100 - 58

7 x ( x - 5 ) = 42

( x - 5 ) = 42 : 7

x - 5 = 6

x = 6 + 5

x = 11

b, 24 + 5 * x = 49

5 * x = 49 - 24

5 * x = 25

x = 25 : 5

x = 5

a, => x ( y + 5 ) - 3 ( y + 5 ) = 7 

   => ( x - 3 )( y+  5 ) = 7 

MÀ  7 = 1.7 = 7.1 = -1.-7 = -7.-1

(+) với x - 3 = 1 và y + 5 = 7 

=> x = 4 và y = 2 

(+) xét tương tự ba trường hợp còn lại 

b, xy + 7x - 4y = 21 

=> x( x + 7 ) - 4y - 28 = 21 - 28 

=> x(x+7) - 4 ( x+ 7 )= -7 

=> ( x - 4 )( x + 7 ) = -7

-7 = 1.-7 = -7.1 = -1.7 = 7.-1

(+) cũng xét 4 TH 

Ban thich co vua lam hay sao ma dat ten la chess vay

\(\left(7x+15\right)-\left(2x-6\right)-21=-125\)

\(\Leftrightarrow7x+15-2x+6=-104\)

\(\Leftrightarrow5x+21=-104\)

\(\Leftrightarrow5x=-125\)

\(\Leftrightarrow x=-25\)

(7x+15)-(2x-6)-21=-125

<=>7x+15-2x+6-21=-125

<=>5x=-125

<=>x=-25

Vậy x=-25

hok tốt

x=-25 nha

a: =>-2x=-8

hay x=4

b: =>7x=-21

hay x=-3

c: =>0,25x=-1,5

hay x=-6

d: =>5,3x=6,36

hay x=6/5

e: =>-4x=-12

hay x=3

f: =>-10x=-10

hay x=1

g: =>2x+2-3-2x=0

=>-1=0(vô lý)

h: =>3-3x+4x-3=0

=>x=0

a,

\(3-x=x-5\\ \Leftrightarrow3x-x+5=0\Leftrightarrow2x+5=0\)

\(\Rightarrow x=-\dfrac{5}{2}\)

b, \(\Rightarrow x=-\dfrac{21}{7}=-3\)

c, \(\Leftrightarrow x=\left(0-1,5\right):0,25=-6\)

a. <=> 2x=8 hay x=4

b.<=> x= -21/7 = -3

c. <=> x= -1,5/ 0,25=-6

d. <=> x= -6,36/-5,3=1,2

e.<=> 4x=12 hay x= 3

f. <=> 10x = 10 hay x = 1

g. <=> 2x +2 = 3 + 2x

<=> 2=3 ( vô lí )

h.<=> 3 - 3x + 4x -3 =0

<=> x=0

a.x²+5x+4

=>x²+4x+x+4

=>x(x+4)+x+4

=>(x+4)(x+1)

b. x²-7x=6

=>x²-x-6x=6

=>x(x-1)-6(x-1)

=>(x-1)(x-6)

c.x²-6x+8

=>x²-2x-4x+8

=>x(x-2)-4(x-2)

=>(x-2)(x-4)

d.x²-10x+21

=>x²-3x-7x+21

=>x(x-3)-7(x-3)

=>(x-3)(x-7)

e.Bạn xem lại í e đi xem có đúng đề không?

g.x²+2x-15

=>x²+5x-3x-15

=>x(x+5)-3(x+5)

=>(x-5)(x-3)

h.x²-3x-28

=>x²+4x-7x-28

=>x(x+4)-7(x+4)

=>(x+4)(x-7)

Nhớ tick cho mình nhé

1, \(x^2+5x+4\)

\(=x^2+x+4x+4\)

\(=x\left(x+1\right)+4\left(x+1\right)\)

\(=\left(x+1\right).\left(x+4\right)\)

2, \(x^2-7x+6\)

\(=x^2-x-6x+6\)

\(=x\left(x-1\right)-6\left(x-1\right)\)

\(=\left(x+1\right)\left(x-6\right)\)

3, \(x^2-6x+8\)

\(=x^2-2x-4x+8\)

\(=x\left(x-2\right)-4\left(x-2\right)\)

\(=\left(x-2\right)\left(x-4\right)\)

4, \(x^2-10x+21\)

\(=x^2-3x-7x+21\)

\(=x\left(x-3\right)-7\left(x-3\right)\)

\(=\left(x-3\right)\left(x-7\right)\)

5, \(x^2-2x+8\)

\(=x^2+2x-4x+8\)

\(=x\left(x+2\right)-4\left(x-2\right)\)

\(=x\left(x+2\right)+4\left(x+2\right)\)

\(=\left(x+2\right)\left(x+4\right)\)

6, \(x^2+2x-15\)

\(=x^2+5x-3x-15\)

\(=x\left(x+5\right)-3\left(x+5\right)\)

\(=\left(x+5\right)\left(x-3\right)\)

7, \(x^2-3x-28\)

\(=x^2+4x-7x-28\)

\(=x\left(x+4\right)-7\left(x+4\right)\)

\(=\left(x+4\right)\left(x-7\right)\)

a) \(x^2+5x+4\)

\(=x^2+x+4x+4\)

\(=x\left(x+1\right)+4\left(x+1\right)\)

\(=\left(x+4\right)\left(x+1\right)\)

b) \(x^2-7x+6\)

\(=x^2-x-6x+6\)

\(=x\left(x-1\right)-6\left(x-1\right)\)

\(=\left(x-6\right)\left(x-1\right)\)

c) \(x^2-6x+8\)

\(=x^2-2x-4x+8\)

\(=x\left(x-2\right)-4\left(x-2\right)\)

\(=\left(x-4\right)\left(x-2\right)\)

d) \(x^2-10x+21\)

\(=x^2-3x-7x+21\)

\(=x\left(x-3\right)-7\left(x-3\right)\)

\(=\left(x-7\right)\left(x-3\right)\)

e) \(x^2-2x-8\)

\(=x^2-2x-4-4\)

\(=\left(x-2\right)\left(x+2\right)-2\left(x+2\right)\)

\(=\left(x-2-2\right)\left(x+2\right)=\left(x-4\right)\left(x+2\right)\)

f) \(x^2+2x-15\)

\(=x^2+5x-3x+15\)

\(=x\left(x+5\right)-3\left(x+5\right)\)

\(=\left(x-3\right)\left(x+5\right)\)

g) \(x^2-3x-28\)

\(=x^2+7x-4x-28\)

\(=x\left(x+7\right)-4\left(x+7\right)\)

\(=\left(x-4\right)\left(x+7\right)\)