What is centroid based clustering? Why is k-means clustering called a centroid based clustering algorithm? Cluster the following instances of given data with the help of K means algorithm (Take K = 2, use first and last data points as initial centroids):

Instance	X	Y
P1	2	3
P2	3	4
P3	6	8
P4	7	9
P5	8	10
P6	9	11