Bonsoir,
B = 1/3 - 4/3 x 2/5
B = 1/3 - 8/15
B = (1 x 5) / (3 x 5) - 8/15
B = 5/15 - 8/15
B = - 3/15
B = (3 x - 1) / (3 x 5)
B = - 1/5
C = (3/4 + 1/2) : (2/5 - 5/2)
C = [3/4 + (1 x 2) / (2 x 2)] : [(2 x 2) / (5 x 2) - (5 x 5) / (2 x 5)]
C = (3/4 + 2/4) : (4/10 - 25/10)
C = 5/4 : - 21/10
C = 5/4 x - 10/21
C = - 20/84
C = (4 x - 5) / (4 x 21)
C = - 5/21.