Titik K(2,7),L(-1,-2),dan M(a,10) terletak pada satu garis lurus. Nilai a adalah.... a. -5. c. 3 b. -2. d. 18

y-y1 x-x1
------- = --------
y2-y1 x2-x1

y-7 x-2
------ = --------
-2-7 -1-2

y-7 x-2
----- = --------
-9 -3

y-7 x-2
----- = --------
3 1

y-7 = 3 (x-2)
y-7 = 3x - 6
y= 3x -6 +7
y= 3x+1 (titik k dan L)

Titik M (a,10)
--> y= 3x+1
10 = 3x +1
-3x= 1-10
x= -9 : -3
(a) x = 3.