\(x+3=12\\ \Rightarrow x=9\)

Vậy \(x=9\).

\(4x+3x=30-20:10\\ \Rightarrow x\left(4+3\right)=30-2\\ \Rightarrow x.7=28\\ \Rightarrow x=4\)

Vậy \(x=4.\)

cứu tôi đây là tìm x thuộc n

đây là tìm x thuộc N

4x + 3x = 30 – 20 : 10

7x = 30 - 2

7x = 28

x = 28 : 7

x = 4

b)

4x + 3x = 30 – 20 : 10

7x = 30 - 2

7x = 28

x = 28 : 7

x = 4

7x=28

x=4

bạn nào bít giúp mik vr

\(4x+3x=30-20:10\)

\(4x+3x=30-2\)

\(4x+3x=28\)

\(\left(4+3\right)x=28\)

\(7x=28\)

\(x=28:7\)

\(x=4\)

Vậy \(x=4\)

Chúc cậu học tốt !!!

a) (x - 3) : 2 = 5 14  :  5 12

(x - 3) : 2 = 5 2

(x - 3) : 2 = 25

(x - 3) = 25.2

x = 50 + 3

x = 53

b) 4x + 3x = 30 – 20 : 10

7x = 30 - 2

7x = 28

x = 28 : 7

x = 4

1) Ta có: \(5\left(x-2\right)=3x+10\)

\(\Leftrightarrow5x-10-3x-10=0\)

\(\Leftrightarrow2x-20=0\)

\(\Leftrightarrow2\left(x-10\right)=0\)

Vì 2>0

nên x-10=0

hay x=10

Vậy: x=10

2) Ta có: \(x^2\left(x-5\right)-4x+20=0\)

\(\Leftrightarrow x^2\left(x-5\right)-4\left(x-5\right)=0\)

\(\Leftrightarrow\left(x-5\right)\left(x^2-4\right)=0\)

\(\Leftrightarrow\left(x-5\right)\left(x-2\right)\left(x+2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-5=0\\x-2=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=5\\x=2\\x=-2\end{matrix}\right.\)

Vậy: x∈{-2;2;5}

3) Ta có: \(\frac{3x+1}{4}+\frac{8x-21}{20}=\frac{3\left(x+2\right)}{5}-2\)

\(\Leftrightarrow\frac{5\left(3x+1\right)}{20}+\frac{8x-21}{20}-\frac{12\left(x+2\right)}{20}+\frac{40}{20}=0\)

\(\Leftrightarrow15x+5+8x-21-12\left(x+2\right)+40=0\)

\(\Leftrightarrow15x+5-8x-21-12x-24+40=0\)

\(\Leftrightarrow-5x=0\)

hay x=0

Vậy: x=0

4) ĐKXĐ: x≠5; x≠-5

Ta có: \(\frac{3}{4x-20}+\frac{7}{6x+30}=\frac{15}{2x^2-50}\)

\(\Leftrightarrow\frac{3}{4\left(x-5\right)}+\frac{7}{6\left(x+5\right)}-\frac{15}{2\left(x-5\right)\left(x+5\right)}=0\)

\(\Leftrightarrow\frac{9\left(x+5\right)}{12\left(x-5\right)\left(x+5\right)}+\frac{14\left(x-5\right)}{12\left(x+5\right)\left(x-5\right)}-\frac{180}{12\left(x-5\right)\left(x+5\right)}=0\)

\(\Leftrightarrow9x+45+14x-70-180=0\)

\(\Leftrightarrow23x-205=0\)

\(\Leftrightarrow23x=205\)

hay \(x=\frac{205}{23}\)(tm)

Vậy: \(x=\frac{205}{23}\)

1) 4x-(2x-5)=21

4x-2x+5=21

2x+5=21

2x=21 -5

2x=16

x=16/2

x=8

2)14x+5=8x+10

14x-8x=10-5

6x=5

x=5/6

3) 15+5x=3x+30

5x-3x=30-15

2x=15

x=15/2

Vậy x=15/2

a)   | x + 10 | - ( 5 - 3x ) = ( 4x - 10 ) - ( x - 5 )

=>                   | x + 10 | = ( 5 - 3x ) + ( 4x - 10 ) - ( x - 5 )

=>                   | x + 10 | = 5 - 3x + 4x - 10 - x + 5

=>                   | x +10 | = 0

=>                     x + 10 = 0

=>                      x = -10

              Vậy...

b) Làm tương tự 

Kết quả : | 3x + 21 | = -10  ( vô lí)       ( vì |3x+21| >= 0 mà -10<0)

Vậy không tìm được x thỏa mãn bài toán

a) x+3=12

x=12-3

x=9

b)(x-3):2=5¹⁴:5¹²

=>(x-3):2=5²

=>(x-3):2=25

=>x-3=25.2

=>x-3=50

=>x=50+3

=>x=53

c)4x+3x=30-20:10

=>x(4+3)=30-2

=>7x=28

=>x=28:7

=>x=4

d)2x-138=2³.3²

=>2x-138=8.9

=>2x-138=72

=>2x=72+138

=>2x=210

=>x=210:2

=>x=105

a) x + 3 = 12

x = 12 - 3

x = 9

b) ( x - 3 ) : 2 = 5¹⁴ : 5¹²

( x - 3 ) : 2 = 5^14-12

( x - 3 ) : 2 = 5²

( x - 3 ) : 2 = 25

x - 3 = 50

x = 53

c) 4x + 3x = 30 - 20 : 10

7x = 28

x = 4

d) 2x - 138 = 2³ x 3²

2x - 138 = 8 x 9

2x - 138 = 72

2x = 210

x = 105