Bonjour,
a) (2x+1)(x+3)
= 2x² +6x +x +3
= 2x² +7x +3
b) (x+1)(x-1)
= x² -x +x -1
= x² -1
c) (2x-3)(2x+1)
= 4x² +2x -6x -3
= 4x² -4x -3
d) (1-2x)(x+2)
= x +2 -2x² -4x
= -2x² -3x +2
Exercices supplémentaires
a) 19×21=399
b) 18x22 = 396
c) 98×102 = 9 996
d) (x-1)(x+1)
= x² +x -x -1
= x² - 1