a,

\(x=\left\{0;5;10;15;20;25\right\}\)

b.

\(x=\left\{20,30,40,50,60\right\}\)

x ϵ A = {  25; 20; 15; 10; 5; 0;....;}

x ϵ A = { x =5k/kϵZ; k< 6}

   1,53 x 82 + 8,2 x 15,3 + 1,53 x 22 - 1,53 x 86

=15,3 x 8,2 + 8,2 x 15,3 + 15,3  x 2,2 -  15,3 x 8,6

= 15,3 (8,2 + 8,2 + 2,2 - 8,6)

= 15,3 . 10

=153

\(6^2:x-1=2^3\\ 36:x-1=8\\ 36:x=8+1\\ 36:x=9\\ x=36:9\\ x=4.\)

\(^{^{ }}\)6^2:x-1=2^3
x-1=6^2:2^3
x-1=36:8

x-1=9/2

x=9/2-1

x=7/2

Vậy x=7/2

\(2.x-5=13\\ 2.x=13+5\\ 2.x=18\\ x=18:2\\ x=9.\)

2.x - 5 = 13

2.x = 13 + 5

2.x = 18

x = 18 : 2

x = 9

x-65=38-58

=> x-65=-20

=> x = 45

\(x-65=38-58\)

\(x-65=-20\)

\(x=-20+65=65-20\)

\(x=45\)

91 - 5 x ( 5 + x ) = 61

5 x ( 5 + x ) = 91 - 61

5 x ( 5 + x ) = 30

5 + x = 30 : 5

 5 + x = 6

x = 6 - 5

x = 1

36 = 2² . 3²

72 = 2³ . 3²

ƯCLN(36; 72) = 2² . 3² = 36

Vì 72 chia hết cho 36 => ƯCLN(72,36) = 36

`2^(x+1)-2^x =32`

`2^x (2-1)=32`

`2^x * 1 =32`

`2^x=32/1=32`

`2^x=2^5`

`=> x=5`

2^x+1- 2^x = 32

2^x.2 - 2^x = 2⁵

2^x.(2-1) = 2⁵

2^x.1=2⁵

2^x = 2⁵

x = 5

=[1800 - ( 64 - 54 )³ ]:8 + 22

=   (1800 - 1000):8+22

=800:8+22

=100+22=122

\(5\cdot2^2+\left(x+3\right)=5^2\)

\(5\cdot4+\left(x+3\right)=25\)

\(20+\left(x+3\right)=25\)

\(x+3=25-20\)

\(x+3=5\)

\(x=5-3\)

\(x=2\)

5.\(2^2\)+(x+3)=\(5^2\)

=>5.4+x+3=25

=>x=25-3-20

=>x=2