Đáp án:

`1.`

`8^(x+3) +2^(3x)-2^9=2^18`

`=>(2^3)^(x+3)+2^(3x)=2^18+2^9`

`=>2^(3x+9)+2^(3x)=262144+512`

`=>2^(3x) *2^9 +2^(3x)=262656`

`=>2^(3x)*(2^9 +1)=262656`

`=>2^(3x) *513=262656`

`=>2^(3x)=262656:513`

`=>2^(3x)=512`

`=>2^(3x)=2^9`

`=>3x=9`

`=>x=9:3`

`=>x=3`

Vậy: `x=3`

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