Gasiti x si y stiind ca 13(x)+31(y)=23



Răspuns :

13(x)+31(y)=23
13(x)=x+3;  x>3
31(y)=3y+1;  y>3
=> x+3+3y+1=23
x+3y=23-4
x+3y=19
pt y=4 => x+3·4=19; x=19-12
x=7
pt y=5 => x+3·5=19; x=19-15
x=4

R: x=4 si y=5
     x=7 si y=4
verificare: 13(4)+31(5)=4+3+3·5+1=23 (A)
                 13(7)+31(4)=7+3+3·4+1=23 (A)