(15 x 14 - 1)/(13 x 15 + 14)
= (15 . 13 + 15 - 1)/(13 . 15 + 14)
= (15 . 13 + 14)/(13 . 15 + 14)
= 1

627x629-1/626+627x628
= (627.628 + 627 - 1)/(626 + 627.628)
= (627.628 + 626)/(626 + 627.628)
= 1

(15x14-1) : (13x15+14)
= [ 15 x (13+1)-1] : (15x13+14)
= (15 x 13 + 15 -1 ) : (15x13+14)
= (15 x 13 + 14 ) : (15 x 13 + 14 )
=    1
537x639-1/536+537x538

627x629-1/626+627x628

627x629-1/626+627x628
= (627.628 + 627 - 1)/(626 + 627.628)
= (627.628 + 626)/(626 + 627.628)
= 1

(15 x 14 - 1)/(13 x 15 + 14)
= [15 × (13 + 1) - 1](13 x 15 + 14)
= (15 × 13 + 15 - 1)/(13 x 15 + 14)
= (13 x 15 + 14)/(13 x 15 + 14)
= 1
*Cách khác: 
(15 x 14 - 1)/(13 x 15 + 14)
= (15 x 14 - 1)/[(14 - 1) × 15 + 14]
= (15 x 14 - 1)/(14 × 15 - 15 + 14)
= (15 x 14 - 1)/(15 x 14 - 1)
= 1
 

(537 x 639 - 1)/(536 + 537 x 538)
= [537 × (638 + 1) - 1]/(536 + 537 x 538)
= (537 × 638 + 537 - 1)/(536 + 537 x 538)
= (537 × 638 + 536)/(536 + 537 x 538)
= 1
*Cách khác:
(537 x 639 - 1)/(536 + 537 x 538)
= (537 x 639 - 1)/[535 + 537 × (539 - 1)]
= (537 x 639 - 1)/(537 x 639 - 537 + 536)
= (537 x 639 - 1)/(537 x 639 - 1)
= 1

 

(627 x 629 - 1)/(626 + 627 x 628)
= [627 × (628 + 1) - 1]/(626 + 627 x 628)
= (627 × 628 + 627 - 1)/(626 + 627 x 628)
= (626 + 627 x 628)/(626 + 627 x 628)
​= 1
*Cách khác: 
(627 x 629 - 1)/(626 + 627 x 628)
= (627 x 629 - 1)/[626 + 627 x (629 - 1)]
=  (627 x 629 - 1)/(626 + 627 × 629 - 627)
=  (627 x 629 - 1)/(627 x 629 - 1)
= 1

627x629-1/626+627x628
= (627.628 + 627 - 1)/(626 + 627.628)
= (627.628 + 626)/(626 + 627.628)
= 1