`a ) B = 31 . 26 - 10`
`B = 31 . ( 25 + 1 ) - 10`
`B = 31 . 25 + (31 - 10)`
`B = 31 . 25 + 21`
`B = ( 30 + 1 ) . 25 + 21`
`B = 30 . 25 + ( 25 + 21)`
`B = 30 . 25 + 46`
Vì `25 . 30 + 10 < 30 . 25 + 46` nên `A < B`
`b ) D = 453 . 138 - 110`
`D = 453 . ( 137 + 1 ) - 110`
`D = 453 . 137 + (453 - 110)`
`D = 453 . 137 + 343`
`D = ( 454 - 1 ) . 137 + 343`
`D = 454 . 137 + ( 343 - 137 )`
`D = 454 . 137 + 206`
Vì `137 . 454 + 206 = 454 . 137 + 206` nên `A = B`
`#dtkc`