Question

Resolva o sistema x+y=84 x-y=34

Answer 1

x + y = 84
x - y = 34 --> x = 34 + y (substitui na primeira)

34 + y + y = 84 --> 34 + 2y = 84 --> 2y = 84 - 34 --> 2y = 50 --> y = 25

x = 34 + y --> x = 34 + 35 --> x = 69

Answer 2

x+y=84
x-y=34       " y - y = 0y"

2x  = 118
x = 118 / 2
x = 59

59 + y = 84
y = 84 - 59
y = 25

S{ 59 e 25