Assertion: The points (k-1, k+2), (k, k+1) and (k+1, k) are collinear for any value of k.
Reason: Three points A, B, C are collinear if slope of AB is equal to slope of BC.
(1)
Slope of line passing through (k-1, k+2) and (k, k+1) is m1=k+1-k-2k-k+1=-1 (independent of k)
Slope of line passing through (k, k+1) and (k+1, k) is m2=k-k-1k+1-k=-1 (independent of k)
∵ m1=m2
∴ Points (k-1, k+2), (k, k+1) and (k+1, k) are collinear, for any value of k.