In the diagram, < WOZ = 180o (angle on a straight line)
< WOX = < XOY = < YOZ
(|WX| = |XY| = |YZ|)
180o3 = 60o
= 60o
M + m =2m (base angles of isosceles △, |OY| and |OZ| are radii)
< YOZ + 2m (base angles of a △)
60o + 2m = 180o (sum of a △)
60o + 2m = 180o
2m = 180o - 60o
2m = 120o
m = 120o2