bonjour
A = x² + 6 x + 9
B = x² + 3 x - 2x - 6 = x² + x - 6
C = x² - 14 x + 49
D = x² - 16
81 ² = ( 80 + 1 ) ( 80 + 1 ) = 6 400 + 80 + 80 + 1 = 6 561
63² - 61 ² = ( 63 - 61 ) ( 63 + 61 ) = 3 969 - 3 721 = 248
48 ² = ( 50 -2 )² = 2 500 - 200 + 4 = 2 304
49 x 51 ( 50 - 1 ) ( 50 + 1 ) = 2 500 - 1 = 2 499