Tìm x a)5^x.5^3=125^2.25^3 b)(-1/4)^x-2=1/64 c) (x-3/4)^2=49/81

Đáp án:

`a)`

` 5^(x) * 5^3 = 125^2 * 25^3`

` => 5^(x) * 5^3 = (5^3)^2 * (5^2)^3`

` => 5^(x+3) = 5^6 * 5^6  = 5^12`

` => x +3 = 12`

` => x= 9` 

`b)`

` (-1/4)^(x-2) = 1/64 = (-1/4)^4` 

` => x-2 = 4`

` => x= 6`

`c)`

` (x-3/4)^2 = 49/81 = (7/9)^2 = -7/9`

TH1

` x-3/4 = 7/9`

` => x= 7/9 +3/4 = 55/36`

TH2

` x-3/4 = -7/9`

` => x= -7/9 +3/4`

` => x= -1/36`

Vậy ` x= 55/36` hoặc ` x=-1/36`