garis 7x + 2y = -13 dan 8x - 3y = -36 berpotongan di titik (p,q+1). Nilai p-q = ...

7x + 2y = -13  (x3)
8x - 3y = -36   (x2)
--------------------------
21x + 6y = -39
16x - 6y = -72
-------------------------- +
37x = -111
x = -111 / 37
x = -3

7x + 2y = -13
7(-3) + 2y = -13
-21 + 2y = -13
2y = -13 + 21
2y = 8
y = 4

titik potongnya (p, q+1) = (-3, 4)
p = x
p = -3

q + 1 = y
q + 1 = 4
q = 4 - 1
q = 3

nilai p - q = -3 - 3 = -6