trig
posted by Grail .
From the top of a hill 700 ft. high, an observer notes that the angles of depression of two successive markerstones on a level ground, which leads straight away from the hill are 5 degree and 15 degree respectively. Find the distance between the two markerstones.

tan 15 = 700/D1
tan 5 = 700/D2
find D1 and D2
subtract