Question

Determinati numerele reale x si y astfel incat x-y=5 si x+y=7.

Answer 1

x-y+x+y=5+7
2x=12
x=12:2=6
6+y=7=>y=1

Answer 2

x-y=5
x+y=7
5+7=2x
12=2x
x=6
7-6=1 sau 6-5=1 
y=1
verificare:6-1=5
               6+1=7