Now the "right triangular ruler" is placed on the drawing in the following manner: one leg of its right angle passes through ; the vertex of its right angle is placed at a point on the line in such a way that the second leg of the ruler is tangent at to the circle centered at . The value of the angle formed by and is the third of that of the angle to be trisected. It follows that the original angle is trisected by the line , and the parallel to passing through .