Răspuns:
a) 13/3; b) 89/40.
Explicație pas cu pas:
5/x=8/y => 8x=5y adica x=5y/8
a)
calculam numaratorul: x+y=5y/8+y=13y/8
calculam numitorul: y-x=y-5y/8=3y/8
(x+y)/(y-x)=(13y/8):(3y/8)=13y/8*8/3y=13/3
b) calculam numaratorul: (^2 inseamna ridicat la puterea a2-a
iar * =inmultire)
x^2+y^2=(5y/8)^2+y^2=25y^2/64+y^2=89y^2/64
calculam numitorul: x*y=5y/8*y=5y^2/8
(x^2+y^2)/x*y=(89y^2/64):(5y^2/8)=89y^2/64*8/5y^2=89/40
