Diketahui garis l bergradien -1/2 dan melalui titik (2,-3) jika titik (a,5) dan (-1,b) terletak pada garis l tentukan nilai a+b.

m = -1/2

melalui (2, -3)
x1 = 2
y1 = -3

(y - y1) = m(x - x1)
(y - (-3)) = -1/2(x - 2)
(y + 3) = -1/2(x - 2)
2(y + 3) = -x + 2
2y + 6 = -x + 2
x + 2y + 6 - 2 = 0
x + 2y + 4 = 0

Persamaan garis l
x + 2y + 4 = 0

titik (a, 5)
a + 2(5) + 4 = 0
a + 10 + 4 = 0
a + 14 = 0
a = -14

titik (-1, b)
-1 + 2(b) + 4 = 0
2b + 3 = 0
b = -3/2

maka
a + b = -14 - 3/2 = -15 1/2