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Step 3: Without disturbing the radius on the compasses, draw an arc with A as centre
which cuts the first arc at B.

Step 4: Again without disturbing the radius on the compasses and with B as centre, draw an
arc which cuts the first arc at C.

Step 5: red angle whose measure is 120°.

d) CONSTRUCTING A 90° ANGLE
Construct a perpendicular to a line from a point lying on it, this is the required 90° angle.