Tentukan nilai a agar titik (a,2) ,(-1,6) dan(2,3) terlwtak pada suatu garis lurus ? tolong dijawab ya!!!

jawab

m= (y2 -y1)/(x2 - x1)

terletak segaris
m1 = (6-2)/(-1-a)
m2 = (3-6)/(2 +1)

m1 = m2
(6 -2)/(-1 - a) = (3-6)/(2 +1)
4/(-1 - a) = (-3)/(3)
4 (-1 - a) = - 1
-1(-1 - a)= 4
1 + a = 4
a = 3