Răspuns :
a+b=20 a-b=8 a=b+8 b+8+b=20 2b+8=20 2b=20-8 2b=12 b=12:2 b=6 a+6=20 a=20-6 a=14 verific 14+6=20 14-6=8
Se rezolva prin sistem
{x+y=20
x-y=8 <=>
{x=20-y
20-y-y=8 <=>
{x=20-y
-2y=-12 <=>
{x=20-6
y=6 <=>
{x=14
y=6
{x+y=20
x-y=8 <=>
{x=20-y
20-y-y=8 <=>
{x=20-y
-2y=-12 <=>
{x=20-6
y=6 <=>
{x=14
y=6