Question

I need to know that how it construct

Answer 1

firstly you have draw a straight line AB of any length
take A as a centre make a circle of any radius but not more than half of line
take that point as a centre where the circle cut line AB and cut an arc at circle at upper side as e
now join Ae
now it is 60
now again take e as a point cut another arc of same radius on circle at f
join Af
now it is 120
again draw the angle bisector of arc ef at g
join now it is 90