Đáp án:
`a) 112-2^3x=3^3. 27-1`
`=> 112-8x=729-1`
`=> 112-8x=728`
`=> 8x=112-728`
`=> 8x=-616`
`=> x=-616:8`
`=> x=-7`
`b) x vdots 28, x vdots 42, x vdots 12`
`=> x\in BC(28, 42, 12)=B(84)`
`=> x\in {0; 84; 168; 252; 336; ....}`
Mà `250<x<255`
`=> x=252`