Right Triangle For Finding Distance Across a River
Right triangle ABC with angles A, B, C to be used for finding distance across a river. This is a trigonometry problem. Wishing to determine the width of the river, I observed a tree standing directly across on the bank. The angle of elevation of the top of the tree was 32 degrees. At 150 ft. back from this point and in the same direction from the tree the angle of elevation of the top of the tree was 21 degrees. Find the width of the river.
Claude Irwin Palmer Library of Practical Electricity: Practical Mathematics For Home Study (New York: McGraw-Hill Book Company, Inc., 1919) 432
Courtesy the private collection of Roy Winkelman