9) 0,25x : 3= 5/6 : 0,125
0,25x : 3= 6,68
0,25x= 6,68*3
0,25x= 20,04
x= 20,04 : 0,25
x= 80,16
Vậy x= 80,16
10 ) 2^x= 16
=> 2^x= 2^4
Vậy x= 4
11) ( x-5) ^3= -27
(x-5)^3= (-3)^3
=> x-5 = -3
x=(-3)+5
x= 2
Vậy x= 2
12) ( 2x+3)^2= 25
=> ( 2x+3)^2= 5^2
=> 2x+3= 5
2x= 5-3
2x=2
x=2:2
x=1
Vậy x=1