Răspuns :
a+b=12 => a+b=12 =>b-c=-3
a+c=15 /*(-1) => -a-c=-15
b-c=-3 => 2b=10 => b=5 => c=8 => a=7
b+c=13
a+c=15 /*(-1) => -a-c=-15
b-c=-3 => 2b=10 => b=5 => c=8 => a=7
b+c=13
[tex]a+b+b+c+a+c= 12+13+15 \\ 2(a+b+c)=40 \\ a+b+c=40:2=20 \\ c=20-12=8 \\ b=20-15=5 \\ a=20-13=7[/tex]