Take a ruler and a compass and draw a semicircle.

Put the needle of compass on end point of curve in semicircle and draw an arc over the curve .

From the point of intersection of arcs,draw another arc over the curve.
From the point of intersections of arcs ,draw an arc from each in such a way so the arcs intersect and connect the point with centre of line of semicircle and get right angle.
Draw 2 intersecting arcs from one arm's of angle 90 degree's end in semicircle in direction of obtuse angles and another from other end of curved line and creat 135 degree angle and biscect it .