Second: The locus from the inside of the angle (including the vertex) to the points with equal distance on both sides of the angle is the bisector of this angle.
Third: The trajectory of a point whose distance to a fixed point is equal to a fixed length is a circle with the fixed point as the center and the fixed length as the radius.
Fourth: the distance to a straight line is equal to the trajectory of a fixed length point, which is two straight lines parallel to this straight line and with the same distance to this straight line.
Fifth: The locus of points parallel and equidistant to the two parallel lines is a straight line parallel and equidistant to the two parallel lines.
Sixth: The right-angle vertex locus at right angles to the two ends of a line segment is a circle with the diameter of this line segment (except the two ends of this line segment).
Seventh: The locus of a point at an acute angle with both ends of a line segment is the two optimal arcs (except the two ends of this line segment) with this line segment as the chord.