Question

o par ordenado correto do sistem a seguir{2x-7y=12/-2x+5y=-20}e´

Answer 1

{2x-7y=12  (i)
{-2x+5y=-20  (ii)

(ii) +(ii)

-2y=-8  ==>y=4

-2x+5y=-20   ==>-2x+20=-20  ==>x=-40/(-2)=20

Answer 2

{ 2x - 7y = 12>>>>>(×)5
{-2x +5y= -20>>>>(×)7
:
:
{10x - 35y= 60
{-14x+35y= -140
-----------------------(+)
-4x= -80
x=20


2x - 7y= 12
2*20-7y=12
40-7y=12
-7y= 12-40
-7y= - 28
y= 28/7
y= 4



s( 20 , 4 )