 Having three or four lines given in position, it is required to find the locus of points C from which drawing three or four lines to the three or four lines given in position and making given angles with each one of the given lines the following condition holds: the rectangle [or product] of two of the three lines so drawn shall bear a given ratio to the square of the third (if there be only three), or to the rectangle [or product] of the other two (if there be four) (Guicciardini 2009, 54; based on G, 22).