bjr
x/y = 5/8 (1) et y/z = 4/7 (2)
1)
calculer x/z
x/y * y/z = x/z = 5/8 * 4/7 = 5/2 * 1/7 = 5/14
x/z = 5/14
2)
x/z = 5/14 => z/x = 14/5 => 2z/x = 28/5
x/y = 5/8 => y/x = 8/5
(2z - y)/x = 2z/x - y/x = 28/5 - 8/5 = 20/5 = 4
(2z - y)/x = 4