Đáp án:
$-$
Giải thích các bước giải:
a) `B=57xx531`
`=>B=(53+4)xx531`
`=>B=53xx531+4xx531`
`=>B=53xx(571-40)+4xx531`
`=>B=53xx571-53xx40+4xx531`
`=>B=53xx571-53xx4xx10+4xx531`
`=>B=53xx571-530xx4+4xx531`
`=>B=53xx571-(530xx4-4xx531)`
`=>B=53xx571-4xx(530-531)`
`=>B=53xx571+4>53xx571=A`
`=>B>A`
Vậy `A<B`.
b) `B=26xx25251`
`=>B=(25+1)xx25251`
`=>B=25xx25251+25251`
`=>B=25xx(26261-1010)+25251`
`=>B=25xx26261-25xx1010+25251`
`=>B=25xx26261-25250+25251`
`=>B=25xx26261-(25250-25251)`
`=>B=25xx26261+1>25xx26261=A`
`=>B>A`
Vậy `A<B`.