Now we have to draw (112) 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, 1, 2
So, 1 = a/OA, 1 = a/OB, 2 = a/OC
So, OA = a, OB = a and OC = a/2.
or, OA = 2, OB = 2 and OC = 1.

Now we have to draw (120) 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