Garis 2x – y = a dan x + by = 4 berpotongan di titik (2, 1). to

2x – y = a

x + by = 4

titik potong (2 , 1)

a]

2x – y = a

2(2) – 1 = a

4 – 1 = a

a = 3

x + by = 4

2 + b(1) = 4

2 + b = 4

b = 4 – 2

b = 2

jadi nilai a dan b berturut-turut adalah 3 dan 2

b]

2x – y = a

2x – y = 3

y = 2x – 3

m1 = 2

x + by = 4

x + 2y = 4

2y = -x + 4

y = (-x + 4)/2

y = (-1/2)x + 2

m2 = -1/2

m1 × m2 = -1

2 × (-1/2) = -1

-2/2 = -1

-1 = -1

(terbukti kedudukan kedua garis berpotongan tegak lurus)

jadi kedudukan kedua garis berpotongan tegak lurus