Question

Me ajudem a resolver:
{x+y=3
{12x-9y=-20

Answer 1

x + y = 3            (9)
12x - 9y = - 20

9x + 9y = 27
12x - 9y = - 20  (+)
------------------------
       21x =   7
x =    7 (:7)
       -----
        21  (:7)

 x = 1/3

x + y = 3
 
  1    +  y = 3
-----
  3

1 + 3y = 9
---------  -----
    3         3

1 + 3y = 9
3y = 9 - 1
3y = 8
y = 8/3

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