Tentukan penyelesaian sistem persamaan berikut dengan metode subtitusi, untuk x, y ∈ R ! A. x - 3y = 5 dan 3x +2y = -7 B. 2x +2y = -4 dan 6x - 3y= -18 C. 3x - 2

a. x - 3y = 5         |x3
   3x + 2y = -7      |x1
--------------------- (-)
3x - 9y = 15
3x + 2y = -7
---------------------- (-)
-11y = 22, y = -1

3x - 9(-1) = 15
3x + 9 = 15
3x = 15-9 = 6
x = 2
x,y = {2,-1}

b. 2x + 2y = -4   |x3
    6x - 3y = -18  |x1
---------------------- (-)
6x + 6y = -12
6x - 3y = -18
---------------------- (-)
9y = 6, y = 6/9 = 2/3

2x + 2(2/3) = -4
2x + 4/3 = -4
2x = -4 - 4/3 = -12/3 - 4/3 = -16/3
x = -8/3

x,y = {-8/3,2/3)

c. 3x - 2y = 7    |x1
    4x + y = 13   |x2
--------------------- (+)
7x = 20, x = 20/7

3(20/7) - 2y = 7
60/7 - 2y = 7
-2y = 7 - 60/7 = 49/7 - 60/7 = -11/7
y = 11/14

x,y = {20/7,11/14)