Răspuns:
a/b=2/5
5a=2b
a=2b/5
7a-2b/4a + 3b=
[7(2b/5)-2b]/[4(2b/5)+3b]=
(14b/5- 2b)/(8b/5+3b)=
(14b/5-10b/5)/(8b/5+15b/5)=
(4b/5)/(23b/5)=
4b/5×5/23b=
4/23
Explicație pas cu pas:
