 Furthermore, to determine the point C, but one condition is needed, namely, that the product of a certain number of lines shall be equal to, or (what is quite as simple), shall bear a given ratio to the product of certain other lines. Since this condition can be expressed by a single equation in two unknown quantities, we may give any value we please to either \(x\) or \(y\) and find the value of the other from this equation. It is obvious that when not more than five lines are given, the quantity \(x\), which is not used to express the first of the lines can never be of degree higher than the second.