Intecepts on x, y and z axes :-      a, 2a, 3a
The reciprocals of intercepts :-      1/a, 1/2a, 1/3a
Reciprocals are reduced to smallest set of integers by taking LCM :-      6, 3, 2
So, miller indices :-       (6,3,2)

Now we have to draw (1,2,0) plane. Let intecepts by this plane on x, y and z axes are OA, OB

and OC. The reciprocals of intercepts :- 1/OA, 1/OB, 1/OC Reciprocals are reduced to smallest set of integers by taking LCM :- a/OA, a/OB, a/OC But, miller indices of this plane are:- (1,2,0) So, 1 = a/OA, 2 = a/OB, 0 = a/OC So, OA = a, OB = a/2 and OC = infinity i.e plane is parallel to z axis. i.e. OA = 2a, OB = 1a and plane is parallel to z axis. or, OA = 2, OB = 1 and plane is parallel to z axis.

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By :-   Dr. A. W. Pangantiwar