52 VI. ON PARALLELOGRAMS. — ON TRANSLATIONS
Exercise 31. Find the locus of the points such that the sum or diﬀerence of
its distances to two given lines is equal to a given length.
Exercise 32. Given two parallel lines, and two points A, B outside these two
parallels, and on diﬀerent sides, what is the shortest broken line joining the two
points, so that the portion contained between the two parallels has a given direction?