Salut,
A = 37 × 101 = 37 × (100 + 1)
= 37 × 100 + 37 × 1
= 3 700 + 37
= 3 737
B = 21 × 15 = (20 + 1) × 15
= 20 × 15 + 1 × 15
= 300 + 15
= 315
C = 57 × 99 = 57 × (100 - 1)
= 57 × 100 - 57 × 1
= 5 700 - 57
= 5 643
tu essayes de faire le dernier en sachant que 19 = 20 - 1 ?