bonjour
A = 4/7 - 8/42
A = 24/42 - 8/42 = 16 /42 = 8 /21
B = ( 42/24 - 28/24 ) x 9/2
B = 14/24 x 9/2
B = 7/12 x 9/2
B = 63/24 = 21/8
donc ils sont inverses