Răspuns:
13.
x/y = 5/7
x = 5y/7
a)y - x = y - 5y/7 = 7y/7 - 5y/7 = 2y/7
2x = 10y/7
(y - x)/2x = 2y/7 : 10y/7 = 2y/7*7/10y = 1/5
b)x/(y - x) = 5y/y : 2y/7 = 5y/7*7/2y = 5/2
c)x + y = 5y/7 + 7y/7 = 12y/7
2x / (x + y) = 10y/7 : 12y/7 = 10y/7*7/12y = 10/12 = 5/6
d)2y/(x + y) = 2y : 12y/7 = 2y*7/12y = 14y/12y = 14/12 = 7/6
