Tìm x: a)81^-2x.27^x=9^3 b,2^2x+2^x+3=288 c)(x-1/2)^x+2=(x-1/2)x+4 (x thuộc N) help me

`a)`

`81^{-2x}*27^x=9^3`

`=>(3^4)^{-2x}*(3^3)^x=3^6`

`=>3^{-8x}*3^{3x}=3^6`

`=>3^{-5x}=3^6`

`=>-5x=6`

`=>x=-6/5`

Vậy `x=-6/5`

`b)`

`2^{2x}+2^{x}+3=288`

`=>2^{2x}+2^x*2^3=288`

`=>2^{2x}(1+2^3)=288`

`=>2^{2x}*9=288`

`=>2^{2x}=32`

`=>2^{2x}=2^5`

`=>2x=5`

`=>x=5/2`

Vậy `x=5/2`

`c)`

`(x-1/2)^x+2=(x-1/2)^x+4`

`=>(x-1/2)^x-(x-1/2)^x=2+4`

`=>0x=6` `("Vô lí")`

Vậy `x in ∅`