a) 123-5x-5.4=38

123-5x-20=38

103-5x=38

5x=103-38

x=(103-38):5=13

b)

(3.x-16).7^3=2.7^4

3x-16=2.7^4/7^3=2.7=14

3x=14+16=30

x=30/3=10

(3a - 2^4 ).7^3 = 2.7.7^3 

=> 3a - 16 = 2.7 

=> 3a - 16 = 14

=> 3a = 30 

=> a = 10 

a=10                 

\((3.x-2^{4} ):7^3 =2.7^{4}\)

\(=>(3.x-16):7^{3} =2.7^{4}\)

\(=>3.x-16=2.7^{4}:7^{3}\)

\(=>3.x-16=2.7^{4-3}\)

\(=>3.x-16=2.7\)

\(=>3.x-16=14\)

\(=>3.x=14+16\)

\(=>3.x=30\)

\(=>x=30:3\)

\(=>x=10\)

\(\left(3x-2^4\right):7^3=\left(2.7\right)^4\)

\(\Rightarrow\left(3x-2^4\right)=2^4.7^4.7^3\)

\(\Rightarrow3x-2^4=2^4.7^7\)

\(\Rightarrow3x=2^4.7^7+2^4\)

\(\Rightarrow3x=2^4.\left(7^7+1\right)=16\left(7^7+1\right)\)

\(\Rightarrow x=\dfrac{16\left(7^7+1\right)}{3}\)

Sửa lại.

\((3x-2^{4}):7^{3}=2.7^{4}\)

\(=>3x-2^{4} =2.7^{4}.7^{3}\)

\(=>3x-2^{4} =2.7^{7}\)

\(=>3x=2.7^{7}+2^{4}\)

\(=>x=\dfrac{2.7^{7}+16}{3}\)
 

=> 692 - 4 (x⁴ + 17) = 128

=> 4(x⁴ + 17) = 564

=> x⁴ + 17 = 141

=> x⁴ = 124

tới đây là bí rồi

\(\Leftrightarrow3x-16=2.7^4+7^3=5145\Leftrightarrow3x=5161\Leftrightarrow x=\dfrac{5161}{3}\)

\(\left(3x-2^4\right)-7^3=2.7^4\\ \Leftrightarrow\left(3x-16\right)=2.7^4+7^3\\ \Leftrightarrow3x-16=5145\\ \Leftrightarrow3x=5145+16=5161\\ \Leftrightarrow x=\dfrac{5161}{3}\)

(3.x - 2^4) . 7^3 = 2. 7^4

(3.x - 16) . 343 = 2 . 2401

(3.x - 16) . 343 = 4802

3.x - 16 = 4802 : 343 

3.x - 16 = 14

3.x = 14 + 16

3.x = 30

x = 30 : 3

x = 10

=> 3x-2^4 = 2.7

=> 3x - 16 = 14 

=> 3x = 30

=> x = 10

BANG 10 NHE !

( 3x - 2⁴ ) . 7³ = 2.7⁴

=> ( 3x - 16 )  = 2 .( 7⁴ : 7³ )

=> ( 3x - 16 ) = 2 . 7

=> 3x - 16 = 14

=> 3x = 30

=> x = 10

\(\left(3x-2^4\right).7^3=2.7^4\\ \Leftrightarrow3x-16=2.7^4:7^3\\ \Leftrightarrow3x=14+16\\ \Leftrightarrow3x=30\\ \Leftrightarrow x=10\)

Vậy...

\(\left(2x-2^4\right).7^3=2.7^4\)

\(\Leftrightarrow\left(2x-2^4\right)=2.7^4:7^3\)

\(\Leftrightarrow2x-2^4=2.7\)

\(\Leftrightarrow2x-16=14\)

\(\Leftrightarrow2x=30\)

\(\Leftrightarrow x=15\)

Vậy ..

( 3x - 2⁴ ) . 7³ = 2 . 7⁴

( 3x - 16 ) . 343 = 4802

3x - 16 = 4802 : 343

3x - 16 = 14

3x = 14 + 16

3x = 30

x = 30 : 3

x = 10