Răspuns :
a+b=78
a-b=12=> a=12+b
12+b+b=78
2xb=78-12
2xb=66
b=66:2
b=33
a=12+b
a=12+33
a=45
a-b=12=> a=12+b
12+b+b=78
2xb=78-12
2xb=66
b=66:2
b=33
a=12+b
a=12+33
a=45
a+b=78 a-b=12 , inmultim a-b=12 cu -1 =>a+b=78 -a+b=-12 => 2b=12+78 => 2b=90 => b=45 ,a=78-45=33