Bonjour

x = 1 - 1/2 - 2/3 + 3/4

x = (1 x 12) / (1 x 12) - (1 x 6) / (2 x 6) - (2 x 4) / (3 x 4) + (3 x 3) / (4 x 3)

x = 12/12 - 6/12 - 8/12 + 9/12

x = 21/12 - 14/12

x = 7/12

y = 7 x 1/2 - 2/3 x 5/4 + 14/3 x 18/7

y = 7/14 - 10/12 + 252/21

y = 7/14 - 10/12 + (21 x 12) / (21 x 1)

y = (7 x 6) / (14 x 6) - (10 x 7) / (12 x 7) + 12

y = 42/84 - 70/84 + (12 x 84) / (1 x 84)

y = - 28/84 + 1008/84

y = 980/84

y = (28 x 35) / (28 x 3)

y = 35/3.

z = (1 - 1/4) : (2/3 + 2/5)

z = [(1 x 4) / (1 x 4) - 1/4] : [(2 x 5) / (3 x 5) + (2 x 3) / (5 x 3)]

z = (4/4 - 1/4) : (10/15 + 6/15)

z = 3/4 : 16/15

z = 3/4 x 15/16

z = 45/64.