Question

dado o sistema de equacoes
{3x-y=4
{x-y=8 ,
a soma x+y vale:
a)8
b)-6
c)10
d)6
e)-12

Answer 1

{3x-y=4
{x-y=8. x=8+y

3 (8+y)-y=4. x-y=8. x+y=-2-10=-12
24+3y-y=4. x-(-10)=8
3y-y=4-24. x+10=8
2y=-20. x=8-10
y=-20/2. x=-2
y=-10
resposta: e)-12