2. Draw an arc with the same radius at the vertex, point B and point C of angle A. ..
3. Take an arc with an angle of A at the intersection point D and the intersection point B and BC. ..
4. Draw a double arc at the angle A, and take a double arc at the intersection of point C and BC, the intersection point E. ..
5. the intersection of 5.BD and CE (extension line) is point a.