By triangle
1. Put the sloping sides of a triangle such that 45o-45o
coincides with the line 1 which is known and the bottom
detained by the other triangle.
2. Rotate triangle of 45o-45o 90o (see arrows
B) then the hypotenuse will be perpendicular to line l. Sliding
triangles (see arrow b) if necessary.
3. Pull the line m.
Line Tilt
